In planarCopyWrapper, Only copy length, not stride of the last line in the plane

If the destination planes are offset within the destination buffer,
writing the extra bytes at the end may write outside of the destination
buffer.

Originally committed as revision 31746 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale

libswscale/swscale.c

@@ -1663,9 +1663,11 @@ static int planarCopyWrapper(SwsContext *c, const uint8_t* src[], int srcStride[
                     srcPtr+= srcStride[plane];
                     dstPtr+= dstStride[plane];
                 }
-            } else if (dstStride[plane]==srcStride[plane] && srcStride[plane] > 0)
-                memcpy(dst[plane] + dstStride[plane]*y, src[plane], height*dstStride[plane]);
-            else {
+            } else if (dstStride[plane]==srcStride[plane] && srcStride[plane] > 0) {
+                if (height > 0)
+                    memcpy(dst[plane] + dstStride[plane]*y, src[plane],
+                           (height - 1)*dstStride[plane] + length);
+            } else {
                 if(is16BPS(c->srcFormat) && is16BPS(c->dstFormat))
                     length*=2;
                 for (i=0; i<height; i++) {