Don't crash on the function redefinition example

Author: ecprice

mypy/checker.py

@@ -604,8 +604,11 @@ def visit_func_def(self, defn: FuncDef) -> Type:
             else:
                 # Function definition overrides a variable initialized via assignment.
                 orig_type = defn.original_def.type
-                # XXX This can be None, as happens in
-                # test_testcheck_TypeCheckSuite.testRedefinedFunctionInTryWithElse
+                if orig_type is None:
+                    # XXX This can be None, as happens in
+                    # test_testcheck_TypeCheckSuite.testRedefinedFunctionInTryWithElse
+                    self.msg.note("Internal mypy error checking function redefinition.", defn)
+                    return None
                 if isinstance(orig_type, PartialType):
                     if orig_type.type is None:
                         # Ah this is a partial type. Give it the type of the function.