avcodec_align_dimensions2: set only 4 linesizes, not AV_NUM_DATA_POINTERS.

This function is video-only, so there's no point in setting more
linesizes.

Fixes stack corruption in avplay.

libavcodec/utils.c

@@ -219,7 +219,7 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
         *height+=2; // some of the optimized chroma MC reads one line too much
                     // which is also done in mpeg decoders with lowres > 0
 
-    for (i = 0; i < AV_NUM_DATA_POINTERS; i++)
+    for (i = 0; i < 4; i++)
         linesize_align[i] = STRIDE_ALIGN;
 //STRIDE_ALIGN is 8 for SSE* but this does not work for SVQ1 chroma planes
 //we could change STRIDE_ALIGN to 16 for x86/sse but it would increase the
@@ -229,7 +229,7 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
     if(s->codec_id == CODEC_ID_SVQ1 || s->codec_id == CODEC_ID_VP5 ||
        s->codec_id == CODEC_ID_VP6 || s->codec_id == CODEC_ID_VP6F ||
        s->codec_id == CODEC_ID_VP6A) {
-        for (i = 0; i < AV_NUM_DATA_POINTERS; i++)
+        for (i = 0; i < 4; i++)
             linesize_align[i] = 16;
     }
 #endif