Merge "demux.c: remove redundant check" into main

src/webp/decode.h

diff --git a/src/webp/decode.h b/src/webp/decode.h
index e0eaeda..ef6210f 100644
--- a/src/webp/decode.h
+++ b/src/webp/decode.h
@@ -108,7 +108,10 @@
 // Otherwise, output_buffer is returned, for convenience.
 // The parameter 'output_stride' specifies the distance (in bytes)
 // between scanlines. Hence, output_buffer_size is expected to be at least
-// output_stride x picture-height.
+// output_stride x picture-height. A negative stride can be used to flip
+// the image vertically. In this case, the 'output_buffer' should point to
+// the start of the last row of the allocated buffer, and 'output_buffer_size'
+// should be at least abs(output_stride) x picture-height.
 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeRGBAInto(
     const uint8_t* WEBP_COUNTED_BY(data_size) data, size_t data_size,
     uint8_t* WEBP_COUNTED_BY(output_buffer_size) output_buffer,
@@ -140,6 +143,11 @@
 // 'u_size' and 'v_size' respectively.
 // Pointer to the luma plane ('*luma') is returned or NULL if an error occurred
 // during decoding (or because some buffers were found to be too small).
+// Strides can be negative to flip the planes vertically. In this case, the
+// pointers ('luma', 'u', 'v') should point to the start of the last row of
+// the respective buffers. The sizes should be at least abs(luma_stride) x
+// height for the luma plane, and abs(u_stride) x ((height + 1) / 2) and
+// abs(v_stride) x ((height + 1) / 2) for the chroma planes.
 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeYUVInto(
     const uint8_t* WEBP_COUNTED_BY(data_size) data, size_t data_size,
     uint8_t* WEBP_COUNTED_BY(luma_size) luma, size_t luma_size, int luma_stride,