Merge #5603

5603: Fix compilation in video.cpp r=heinrich5991 a=def-

```
/home/deen/isos/ddnet/ddnet-source/src/engine/client/video.cpp:829:9: error: ‘c’ was not declared in this s
cope
  829 |         c->thread_count = 1;
      |         ^
```
<!-- What is the motivation for the changes of this pull request -->

## Checklist

- [ ] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test (especially base/) or added coverage to integration test
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: def <dennis@felsin9.de>

src/engine/client/video.cpp

@@ -826,7 +826,7 @@ bool CVideo::AddStream(OutputStream *pStream, AVFormatContext *pOC, const AVCode
 
 #if defined(CONF_ARCH_IA32) || defined(CONF_ARCH_ARM)
 	// use only 1 ffmpeg thread on 32-bit to save memory
-	c->thread_count = 1;
+	pContext->thread_count = 1;
 #endif
 
 	switch((*ppCodec)->type)