pictor: Correctly check frame dimensions

Fixes: 559/clusterfuzz-testcase-6424225917173760
Bug-Id: CVE-2017-7862
CC: libav-stable@libav.org

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 8c2ea303)
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/pictordec.c

@@ -140,7 +140,7 @@ static int decode_frame(AVCodecContext *avctx,
 
     avctx->pix_fmt = AV_PIX_FMT_PAL8;
 
-    if (s->width != avctx->width && s->height != avctx->height) {
+    if (s->width != avctx->width || s->height != avctx->height) {
         ret = ff_set_dimensions(avctx, s->width, s->height);
         if (ret < 0)
             return ret;