Fix error recovery for multi line strings at the end of the file

test/test_diff_parser.py

@@ -1509,3 +1509,18 @@ def test_async_func2(differ):
         ''')
     differ.initialize(code1)
     differ.parse(code2, parsers=2, copies=1, expect_error_leaves=True)
+
+
+def test_weird_ending(differ):
+    code1 = dedent('''\
+        def foo():
+            a
+            return
+        ''')
+    code2 = dedent('''\
+        def foo():
+            a
+           nonlocal xF"""
+        y"""''')
+    differ.initialize(code1)
+    differ.parse(code2, parsers=1, copies=1, expect_error_leaves=True)