Simplify the regexes

parso/python/diff.py

@@ -388,8 +388,10 @@ class DiffParser(object):
                     # endmarker or another dedented code block.
                     typ, string, start_pos, prefix = next(tokens)
                     if '\n' in prefix or '\r' in prefix:
-                        prefix = re.sub(r'(?<=\n|\r)[^\n\r]+$', '', prefix)
+                        prefix = re.sub(r'[^\n\r]+\Z', '', prefix)
                     else:
+                        # This is basically the next line and it still needs to
+                        # be parserd.
                         prefix = ''
                     yield PythonToken(
                         PythonTokenTypes.ENDMARKER, '',

test/test_diff_parser.py

@@ -955,6 +955,10 @@ def test_wrong_backslash(differ):
     differ.parse(code1, parsers=1, copies=1)
 
 
+def test_comment_change(differ):
+    differ.initialize('')
+
+
 def test_random_unicode_characters(differ):
     """
     Those issues were all found with the fuzzer.
@@ -970,3 +974,4 @@ def test_random_unicode_characters(differ):
     differ.parse(s + '\n', parsers=1, expect_error_leaves=True)
     differ.parse('   result = (\r\f\x17\t\x11res)', parsers=2, expect_error_leaves=True)
     differ.parse('')
+    differ.parse('   a( # xx\ndef', parsers=2, expect_error_leaves=True)