swscale: fix filtersize clipping.

if srcW<=2, clip(x, 1, srcW-2) still allows srcW to be < 1.

libswscale/utils.c

@@ -263,7 +263,8 @@ static int initFilter(int16_t **outFilter, int16_t **filterPos, int *outFilterSi
         if (xInc <= 1<<16)      filterSize= 1 + sizeFactor; // upscale
         else                    filterSize= 1 + (sizeFactor*srcW + dstW - 1)/ dstW;
 
-        filterSize = av_clip(filterSize, 1, srcW - 2);
+        filterSize = FFMIN(filterSize, srcW - 2);
+        filterSize = FFMAX(filterSize, 1);
 
         FF_ALLOC_OR_GOTO(NULL, filter, dstW*sizeof(*filter)*filterSize, fail);