Add more corner cases for M_PARENTHESIS_P

tests/test-mcore.c

@@ -226,6 +226,9 @@ static void test_test(void)
   assert(!M_PARENTHESIS_P(a,b));
   assert(!M_PARENTHESIS_P(a));
   assert(!M_PARENTHESIS_P());
+  assert(!M_PARENTHESIS_P(,));
+  assert(!M_PARENTHESIS_P((),));
+  assert(!M_PARENTHESIS_P(()x));
 }