FFmpeg: Fix failing to record videos with CRF video (fixes #3368)

CHANGES

@@ -18,6 +18,7 @@ Emulation fixes:
 Other fixes:
  - Core: Fix inconsistencies with setting game-specific overrides (fixes mgba.io/i/2963)
  - Debugger: Fix writing to specific segment in command-line debugger
+ - FFmpeg: Fix failing to record videos with CRF video (fixes mgba.io/i/3368)
  - GB Serialize: Prevent loading invalid states where LY >= 144 in modes other than 1
  - GBA: Fix getting game info for multiboot ROMs
  - GBA Core: Fix booting into BIOS when skip BIOS is enabled

src/feature/ffmpeg/ffmpeg-encoder.c

@@ -384,7 +384,9 @@ bool FFmpegEncoderOpen(struct FFmpegEncoder* encoder, const char* outfile) {
 		encoder->videoStream = avformat_new_stream(encoder->context, vcodec);
 		encoder->video = encoder->videoStream->codec;
 #endif
-		encoder->video->bit_rate = encoder->videoBitrate;
+		if (encoder->videoBitrate >= 0) {
+			encoder->video->bit_rate = encoder->videoBitrate;
+		}
 		encoder->video->width = encoder->width;
 		encoder->video->height = encoder->height;
 		encoder->video->time_base = (AVRational) { encoder->frameCycles * encoder->frameskip, encoder->cycles };