lavc/magicyuv: fix undefined behaviour introduced in 8a135a55

Order of evaluation of parameters in C is not defined.

libavcodec/magicyuv.c

@@ -245,7 +245,7 @@ static int decode_frame(AVCodecContext *avctx,
     AVFrame *p = data;
     GetByteContext gb;
     GetBitContext b;
-    int i, j, k;
+    int i, j, k, width, height;
 
     bytestream2_init(&gb, avpkt->data, avpkt->size);
     if (bytestream2_get_le32(&gb) != MKTAG('M','A','G','Y'))
@@ -309,7 +309,9 @@ static int decode_frame(AVCodecContext *avctx,
     s->interlaced = !!(bytestream2_get_byte(&gb) & 2);
     bytestream2_skip(&gb, 3);
 
-    if ((ret = ff_set_dimensions(avctx, bytestream2_get_le32(&gb), bytestream2_get_le32(&gb))) < 0)
+    width  = bytestream2_get_le32(&gb);
+    height = bytestream2_get_le32(&gb);
+    if ((ret = ff_set_dimensions(avctx, width, height)) < 0)
         return ret;
 
     slice_width = bytestream2_get_le32(&gb);