Fix compiler warning in jsonpath_exec.c

Warning was observed in gcc 4.4.6, gcc 4.4.7 and probably others.

Reported-by: Tom Lane
Discussion: https://postgr.es/m/25151.1552751426%40sss.pgh.pa.us

src/backend/utils/adt/jsonpath_exec.c

@@ -1459,15 +1459,11 @@ executePredicate(JsonPathExecContext *cxt, JsonPathItem *pred,
 		JsonbValue *rval;
 		bool		first = true;
 
-		if (rarg)
-		{
 		JsonValueListInitIterator(&rseq, &rseqit);
+		if (rarg)
 			rval = JsonValueListNext(&rseq, &rseqit);
-		}
 		else
-		{
 			rval = NULL;
-		}
 
 		/* Loop over right arg sequence or do single pass otherwise */
 		while (rarg ? (rval != NULL) : first)