We need to fix the extra entity section. This is not a classic entity section.

Example:
[PL1.DXF.gz](https://github.com/LibreDWG/libredwg/files/10702438/PL1.DXF.gz)
[PL1.DWG.gz](https://github.com/LibreDWG/libredwg/files/10702439/PL1.DWG.gz)

Actual output:
```
extra entities: (0x932-0x943 (0), size 17)
==========================================
type: 19 [RCd]
Add entity POLYLINE_2D [23] Decode entity POLYLINE_2D
===========================
Entity number: 23, Type: 19, Addr: 932
flag_r11: 0x80 [RC 0]
          HAS_ATTRIBS(0x80)
size: 9 [RS]
layer: 0 [H(RSd) 8]
opts_r11: 0x1 [RSx 0]
          HAS_FLAG(0x1)
flag: 0x1 [RC 70]
      CLOSED(0x1)

type: 18 [RCd]
Add entity POLYLINE_2D [24] Decode entity POLYLINE_2D
===========================
Entity number: 24, Type: 18, Addr: 93b
flag_r11: 0x0 [RC 0]
size: 8 [RS]
layer: 1306 [H(RSd) 8]
opts_r11: 0x0 [RSx 0]
==========================================
extra entities: end
```

The second item isn't an entity, but extra information for replacement. Every time is 8 bytes in length.
Fix extra entity section in preR13
This is a GitHub Issue
repo:libredwg
owner:LibreDWG
Title : Fix extra entity section in preR13
Issue date:

--- start body ---
We need to fix the extra entity section. This is not a classic entity section.

Example:
[PL1.DXF.gz](https://github.com/LibreDWG/libredwg/files/10702438/PL1.DXF.gz)
[PL1.DWG.gz](https://github.com/LibreDWG/libredwg/files/10702439/PL1.DWG.gz)

Actual output:
```
extra entities: (0x932-0x943 (0), size 17)
==========================================
type: 19 [RCd]
Add entity POLYLINE_2D [23] Decode entity POLYLINE_2D
===========================
Entity number: 23, Type: 19, Addr: 932
flag_r11: 0x80 [RC 0]
          HAS_ATTRIBS(0x80)
size: 9 [RS]
layer: 0 [H(RSd) 8]
opts_r11: 0x1 [RSx 0]
          HAS_FLAG(0x1)
flag: 0x1 [RC 70]
      CLOSED(0x1)

type: 18 [RCd]
Add entity POLYLINE_2D [24] Decode entity POLYLINE_2D
===========================
Entity number: 24, Type: 18, Addr: 93b
flag_r11: 0x0 [RC 0]
size: 8 [RS]
layer: 1306 [H(RSd) 8]
opts_r11: 0x0 [RSx 0]
==========================================
extra entities: end
```

The second item isn't an entity, but extra information for replacement. Every time is 8 bytes in length.
--- end body ---
