swscale/slice: Fix wrong return on error

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

libswscale/slice.c

@@ -288,8 +288,10 @@ int ff_init_filters(SwsContext * c)
     if (!c->desc)
         return AVERROR(ENOMEM);
     c->slice = av_mallocz_array(sizeof(SwsSlice), c->numSlice);
-    if (!c->slice)
+    if (!c->slice) {
+        res = AVERROR(ENOMEM);
         goto cleanup;
+    }
 
     res = alloc_slice(&c->slice[0], c->srcFormat, c->srcH, c->chrSrcH, c->chrSrcHSubSample, c->chrSrcVSubSample, 0);
     if (res < 0) goto cleanup;