avcodec/ffv1dec: Fix end computation with ec=2

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 10e5af15bf)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ffv1dec.c

@@ -347,7 +347,7 @@ static int decode_slice(AVCodecContext *c, void *arg)
     if (f->ac != AC_GOLOMB_RICE && f->version > 2) {
         int v;
         get_rac(&sc->c, (uint8_t[]) { 129 });
-        v = sc->c.bytestream_end - sc->c.bytestream - 2 - 5*f->ec;
+        v = sc->c.bytestream_end - sc->c.bytestream - 2 - 5*!!f->ec;
         if (v) {
             av_log(f->avctx, AV_LOG_ERROR, "bytestream end mismatching by %d\n", v);
             slice_set_damaged(f, sc);