Fix tokenizer: Closing parentheses in the wrong place should not lead to strange behavior

parso/python/tokenize.py

@@ -585,7 +585,8 @@ def tokenize_lines(lines, version_info, start_pos=(1, 0)):
                     if fstring_stack:
                         fstring_stack[-1].close_parentheses(token)
                     else:
-                        paren_level -= 1
+                        if paren_level:
+                            paren_level -= 1
                 elif token == ':' and fstring_stack \
                         and fstring_stack[-1].parentheses_count == 1:
                     fstring_stack[-1].format_spec_count += 1

test/test_tokenize.py

@@ -285,3 +285,17 @@ def test_error_token_after_dedent():
         ERRORTOKEN, NAME, NEWLINE, ENDMARKER
     ]
     assert [t.type for t in lst] == expected
+
+
+def test_brackets_no_indentation():
+    """
+    There used to be an issue that the parentheses counting would go below
+    zero. This should not happen.
+    """
+    code = dedent("""\
+        }
+        {
+          }
+        """)
+    lst = _get_token_list(code)
+    assert [t.type for t in lst] == [OP, NEWLINE, OP, OP, NEWLINE, ENDMARKER]