Fix a backslash issue

parso/python/tokenize.py

@@ -517,7 +517,7 @@ def tokenize_lines(lines, version_info, start_pos=(1, 0)):
                 start = match.end()
                 spos = (lnum, start)
 
-            if new_line and initial not in '\r\n\\#':
+            if new_line and initial not in '\r\n#' and (initial != '\\' or pseudomatch is None):
                 new_line = False
                 if paren_level == 0 and not fstring_stack:
                     i = 0

test/test_diff_parser.py

@@ -1332,3 +1332,19 @@ def test_wrong_indent_in_def(differ):
     differ.initialize(code1)
     differ.parse(code2, parsers=1, expect_error_leaves=True)
     differ.parse(code1, parsers=1)
+
+
+def test_backslash_issue(differ):
+    code1 = dedent('''
+        pre = (
+            '')
+        after = 'instead'
+        ''')
+    code2 = dedent('''
+        pre = (
+            '')
+             \\if 
+        ''')
+    differ.initialize(code1)
+    differ.parse(code2, parsers=1, copies=1, expect_error_leaves=True)
+    differ.parse(code1, parsers=1, copies=1)