A memory leak occurs when makeswf parse a valid swf file, and the filename extension is `.swf`.

## Test Environment
Ubuntu 20.04, 64 bit  
libming (master 04aee52)

## Steps to reproduce
1. compile libming with ASAN
```
$ CC="clang -fsanitize=address,fuzzer-no-link -g" CFLAGS+=" -fcommon" ./configure 
$ make
```
2. Download the poc file from [here](https://raw.githubusercontent.com/Marsman1996/pocs/master/libming/poc-makeswf-04aee52-openswf-leak.swf) and run cmd 
`$ makeswf $POC`

## ASAN report
```
$ ./bin_asan/bin/makeswf ./poc-makeswf-04aee52-openswf-leak.swf
Output file name: out.swf
Output compression level: 9
Output SWF version: 6
Adding prebuilt clip ./poc-makeswf-04aee52-openswf-leak.swf to frame 0... done.
Saving output to out.swf... done.

=================================================================
==1431036==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 88 byte(s) in 1 object(s) allocated from:
    #0 0x4c567f in malloc /home/ubuntu178/Downloads/llvm12/projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x523218 in openswf /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/src/blocks/../../../code/src/blocks/fromswf.c:271:41
    #2 0x5226fe in newSWFPrebuiltClip_fromInput /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/src/blocks/../../../code/src/blocks/fromswf.c:1302:8
    #3 0x4ff753 in embed_swf /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/util/../../code/util/makeswf.c:699:14
    #4 0x4fdd89 in main /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/util/../../code/util/makeswf.c:401:4
    #5 0x7f85ac9be0b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: 88 byte(s) leaked in 1 allocation(s).
```
Memory leak in openswf() at fromswf.c:271
This is a GitHub Issue
repo:libming
owner:libming
Title : Memory leak in openswf() at fromswf.c:271
Issue date:

--- start body ---
A memory leak occurs when makeswf parse a valid swf file, and the filename extension is `.swf`.

## Test Environment
Ubuntu 20.04, 64 bit  
libming (master 04aee52)

## Steps to reproduce
1. compile libming with ASAN
```
$ CC="clang -fsanitize=address,fuzzer-no-link -g" CFLAGS+=" -fcommon" ./configure 
$ make
```
2. Download the poc file from [here](https://raw.githubusercontent.com/Marsman1996/pocs/master/libming/poc-makeswf-04aee52-openswf-leak.swf) and run cmd 
`$ makeswf $POC`

## ASAN report
```
$ ./bin_asan/bin/makeswf ./poc-makeswf-04aee52-openswf-leak.swf
Output file name: out.swf
Output compression level: 9
Output SWF version: 6
Adding prebuilt clip ./poc-makeswf-04aee52-openswf-leak.swf to frame 0... done.
Saving output to out.swf... done.

=================================================================
==1431036==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 88 byte(s) in 1 object(s) allocated from:
    #0 0x4c567f in malloc /home/ubuntu178/Downloads/llvm12/projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x523218 in openswf /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/src/blocks/../../../code/src/blocks/fromswf.c:271:41
    #2 0x5226fe in newSWFPrebuiltClip_fromInput /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/src/blocks/../../../code/src/blocks/fromswf.c:1302:8
    #3 0x4ff753 in embed_swf /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/util/../../code/util/makeswf.c:699:14
    #4 0x4fdd89 in main /home/ubuntu178/cvelibf/test/libming/04aee52/build_asan/util/../../code/util/makeswf.c:401:4
    #5 0x7f85ac9be0b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: 88 byte(s) leaked in 1 allocation(s).
```
--- end body ---
