swscale/swscale: Try to fix rgb48Toxyz12() with slices

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/swscale.c

@@ -978,8 +978,14 @@ int attribute_align_arg sws_scale(struct SwsContext *c,
 
 
     if (c->dstXYZ && !(c->srcXYZ && c->srcW==c->dstW && c->srcH==c->dstH)) {
+        int dstY = c->dstY ? c->dstY : srcSliceY + srcSliceH;
+        av_assert0(dstY >= ret);
+        av_assert0(ret >= 0);
+        av_assert0(c->dstH >= dstY);
+
+        uint16_t *dst16 = (uint16_t*)(dst2[0] + (dstY - ret) * dstStride2[0]);
         /* replace on the same data */
-        rgb48Toxyz12(c, (uint16_t*)dst2[0], (const uint16_t*)dst2[0], dstStride[0]/2, ret);
+        rgb48Toxyz12(c, dst16, dst16, dstStride2[0]/2, ret);
     }
 
     av_free(rgb0_tmp);