Feature: Fix resizing GIF buffer (fixes #695)

CHANGES

@@ -23,6 +23,7 @@ Bugfixes:
  - DS Slot-1: Emulate initial SPI command delay
  - DS: Fix exposed CPU frequencies and audio timing
  - DS Audio: Fix audio sampling slightly too quickly
+ - Feature: Fix resizing GIF buffer (fixes mgba.io/i/695)
 Misc:
  - DS: Set boot complete bit in RAM on boot (fixes mgba.io/i/576, mgba.io/i/580, mgba.io/i/586)
  - DS Memory: Ensure DS9 I/O is 8-byte aligned

src/feature/imagemagick/imagemagick-gif-encoder.c

@@ -102,8 +102,13 @@ static void _magickPostVideoFrame(struct mAVStream* stream, const color_t* pixel
 
 static void _magickVideoDimensionsChanged(struct mAVStream* stream, unsigned width, unsigned height) {
 	struct ImageMagickGIFEncoder* encoder = (struct ImageMagickGIFEncoder*) stream;
+	if (encoder->iwidth == width && encoder->iheight == height) {
+		return;
+	}
+	free(encoder->frame);
 	encoder->iwidth = width;
 	encoder->iheight = height;
+	encoder->frame = malloc(encoder->iwidth * encoder->iheight * 4);
 }
 
 static void _magickVideoFrameRateChanged(struct mAVStream* stream, unsigned numerator, unsigned denominator) {