regexp: fix non greedy quantizers with zero length matches

libregexp.c

@@ -1488,15 +1488,13 @@ static int re_parse_term(REParseState *s, BOOL is_backward_dir)
 
                 if (dbuf_error(&s->byte_code))
                     goto out_of_memory;
+            }
             /* the spec tells that if there is no advance when
                running the atom after the first quant_min times,
                then there is no match. We remove this test when we
                are sure the atom always advances the position. */
             add_zero_advance_check = re_need_check_advance(s->byte_code.buf + last_atom_start,
                                                            s->byte_code.size - last_atom_start);
-            } else {
-                add_zero_advance_check = FALSE;
-            }
 
             {
                 int len, pos;

tests/test_builtin.js

@@ -678,6 +678,8 @@ function test_regexp()
     assert(a, ["a", undefined]);
     a = /(?:|[\w])+([0-9])/.exec("123a23");
     assert(a, ["123a23", "3"]);
+    a = /()*?a/.exec(",");
+    assert(a, null);
 }
 
 function test_symbol()