fix E402 with __all__ var is defined over multiple lines

autopep8.py

@@ -1496,7 +1496,7 @@ def has_future_import(source):
                 return cnt + offset + 1
             return cnt
         elif pycodestyle.DUNDER_REGEX.match(line):
-            continue
+            return cnt
         elif any(line.startswith(kw) for kw in allowed_try_keywords):
             continue
         elif is_string_literal(line):

test/test_autopep8.py

@@ -2524,6 +2524,48 @@ def test_e402_import_some_modules(self):
 )
 a = 1
 print(os, reader, writer)
+"""
+        with autopep8_context(line) as result:
+            self.assertEqual(fixed, result)
+
+    def test_e402_with_dunder(self):
+        line = """\
+__all__ = ["a", "b"]
+def f():
+    pass
+import os
+"""
+        fixed = """\
+import os
+__all__ = ["a", "b"]
+
+
+def f():
+    pass
+"""
+        with autopep8_context(line) as result:
+            self.assertEqual(fixed, result)
+
+    def test_e402_with_dunder_lines(self):
+        line = """\
+__all__ = [
+    "a",
+    "b",
+]
+def f():
+    pass
+import os
+"""
+        fixed = """\
+import os
+__all__ = [
+    "a",
+    "b",
+]
+
+
+def f():
+    pass
 """
         with autopep8_context(line) as result:
             self.assertEqual(fixed, result)