It's a heap-buffer-overflow bug caused by missing '\0' check of the end of URI.

Step to reproduce:
```
1.get latest commit code (MP4Box - GPAC version 1.1.0-DEV-rev1169-gbbd741e-master)
2.compile with sanitizer 
./configure --enable-sanitizer 
make
3.run ./MP4BOX -hint poc -out /dev/null
```

Env:
Ubunut 20.04 , clang 10.0.0

ASAN report
```
==1622396==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61f00000601b at pc 0x7fedb9f66fbf bp 0x7fff337013a0 sp 0x7fff33701390
READ of size 1 at 0x61f00000601b thread T0
    #0 0x7fedb9f66fbe in gp_rtp_builder_do_mpeg12_video ietf/rtp_pck_mpeg12.c:160
    #1 0x7fedba84857b in gf_hinter_track_process media_tools/isom_hinter.c:808
    #2 0x563ebe335eb7 in HintFile /home/lly/pro/gpac_public/applications/mp4box/main.c:3531
    #3 0x563ebe341eec in mp4boxMain /home/lly/pro/gpac_public/applications/mp4box/main.c:6329
    #4 0x7fedb94800b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #5 0x563ebe308bdd in _start (/home/lly/pro/gpac_public/bin/gcc/MP4Box+0x4abdd)

0x61f00000601b is located 0 bytes to the right of 2971-byte region [0x61f000005480,0x61f00000601b)
allocated by thread T0 here:
    #0 0x7fedbc59cbc8 in malloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dbc8)
    #1 0x7fedba331c30 in Media_GetSample isomedia/media.c:617

SUMMARY: AddressSanitizer: heap-buffer-overflow ietf/rtp_pck_mpeg12.c:160 in gp_rtp_builder_do_mpeg12_video
Shadow bytes around the buggy address:
  0x0c3e7fff8bb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8bc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8bd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8be0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8bf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c3e7fff8c00: 00 00 00[03]fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c50: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
```
[poc.zip](https://github.com/gpac/gpac/files/7012523/poc.zip)

Bug: heap-buffer-overflow in gp_rtp_builder_do_mpeg12_video
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Bug: heap-buffer-overflow in gp_rtp_builder_do_mpeg12_video
Issue date:

--- start body ---
It's a heap-buffer-overflow bug caused by missing '\0' check of the end of URI.

Step to reproduce:
```
1.get latest commit code (MP4Box - GPAC version 1.1.0-DEV-rev1169-gbbd741e-master)
2.compile with sanitizer 
./configure --enable-sanitizer 
make
3.run ./MP4BOX -hint poc -out /dev/null
```

Env:
Ubunut 20.04 , clang 10.0.0

ASAN report
```
==1622396==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61f00000601b at pc 0x7fedb9f66fbf bp 0x7fff337013a0 sp 0x7fff33701390
READ of size 1 at 0x61f00000601b thread T0
    #0 0x7fedb9f66fbe in gp_rtp_builder_do_mpeg12_video ietf/rtp_pck_mpeg12.c:160
    #1 0x7fedba84857b in gf_hinter_track_process media_tools/isom_hinter.c:808
    #2 0x563ebe335eb7 in HintFile /home/lly/pro/gpac_public/applications/mp4box/main.c:3531
    #3 0x563ebe341eec in mp4boxMain /home/lly/pro/gpac_public/applications/mp4box/main.c:6329
    #4 0x7fedb94800b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #5 0x563ebe308bdd in _start (/home/lly/pro/gpac_public/bin/gcc/MP4Box+0x4abdd)

0x61f00000601b is located 0 bytes to the right of 2971-byte region [0x61f000005480,0x61f00000601b)
allocated by thread T0 here:
    #0 0x7fedbc59cbc8 in malloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dbc8)
    #1 0x7fedba331c30 in Media_GetSample isomedia/media.c:617

SUMMARY: AddressSanitizer: heap-buffer-overflow ietf/rtp_pck_mpeg12.c:160 in gp_rtp_builder_do_mpeg12_video
Shadow bytes around the buggy address:
  0x0c3e7fff8bb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8bc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8bd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8be0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c3e7fff8bf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c3e7fff8c00: 00 00 00[03]fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c3e7fff8c50: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
```
[poc.zip](https://github.com/gpac/gpac/files/7012523/poc.zip)

--- end body ---
