avcodec/exr: set layer_match in all branches

Otherwise it is left to the value from the previous iteration
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 433d2ae4)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/exr.c

@@ -1389,6 +1389,7 @@ static int decode_header(EXRContext *s, AVFrame *frame)
                         if (*ch_gb.buffer == '.')
                             ch_gb.buffer++;         /* skip dot if not given */
                     } else {
+                        layer_match = 0;
                         av_log(s->avctx, AV_LOG_INFO,
                                "Channel doesn't match layer : %s.\n", ch_gb.buffer);
                     }