Fix some boolean logic (#2737)

Author: vrabaud

src/read.c

@@ -6699,7 +6699,8 @@ static avifResult avifDecoderApplySampleTransform(const avifDecoder * decoder, a
         return result;
     }
 
-    for (avifBool alpha = AVIF_FALSE; alpha <= decoder->alphaPresent ? AVIF_TRUE : AVIF_FALSE; ++alpha) {
+    for (int pass = 0; pass < (decoder->alphaPresent ? 2 : 1); ++pass) {
+        avifBool alpha = (pass == 0) ? AVIF_FALSE : AVIF_TRUE;
         AVIF_ASSERT_OR_RETURN(decoder->data->sampleTransformNumInputImageItems <= AVIF_SAMPLE_TRANSFORM_MAX_NUM_INPUT_IMAGE_ITEMS);
         const avifImage * inputImages[AVIF_SAMPLE_TRANSFORM_MAX_NUM_INPUT_IMAGE_ITEMS];
         for (uint32_t i = 0; i < decoder->data->sampleTransformNumInputImageItems; ++i) {

src/write.c

@@ -975,10 +975,10 @@ static avifBool avifGainMapIdenticalChannels(const avifGainMap * gainMap)
 }
 
 // Returns the number of bytes written by avifWriteGainmapMetadata().
-static avifBool avifGainMapMetadataSize(const avifGainMap * gainMap)
+static uint32_t avifGainMapMetadataSize(const avifGainMap * gainMap)
 {
     const uint8_t channelCount = avifGainMapIdenticalChannels(gainMap) ? 1u : 3u;
-    return sizeof(uint16_t) * 2 + sizeof(uint8_t) + sizeof(uint32_t) * 4 + channelCount * sizeof(uint32_t) * 10;
+    return (uint32_t)(sizeof(uint16_t) * 2 + sizeof(uint8_t) + sizeof(uint32_t) * 4 + channelCount * sizeof(uint32_t) * 10);
 }
 
 static avifResult avifWriteGainmapMetadata(avifRWStream * s, const avifGainMap * gainMap, avifDiagnostics * diag)