fftools/cmdutils: Add protective () to FLAGS

issue found while reviewing CID1452612 Free of array-typed value

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit d9b9fc4be2)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

fftools/cmdutils.c

@@ -581,7 +581,7 @@ static const AVOption *opt_find(void *obj, const char *name, const char *unit,
     return o;
 }
 
-#define FLAGS (o->type == AV_OPT_TYPE_FLAGS && (arg[0]=='-' || arg[0]=='+')) ? AV_DICT_APPEND : 0
+#define FLAGS ((o->type == AV_OPT_TYPE_FLAGS && (arg[0]=='-' || arg[0]=='+')) ? AV_DICT_APPEND : 0)
 int opt_default(void *optctx, const char *opt, const char *arg)
 {
     const AVOption *o;