fix in-place operations again: type inference may not work in advance

Cython/Compiler/ExprNodes.py

@@ -704,7 +704,7 @@ class ExprNode(Node):
         return self.result_in_temp()
 
     def may_be_none(self):
-        if not self.type.is_pyobject:
+        if self.type and not self.type.is_pyobject:
             return False
         if self.constant_result not in (not_a_constant, constant_value_not_set):
             return self.constant_result is not None
@@ -1530,7 +1530,7 @@ class NameNode(AtomicExprNode):
         return 1
 
     def may_be_none(self):
-        if self.type.is_pyobject and self.cf_state:
+        if self.cf_state and self.type and self.type.is_pyobject:
             # gard against infinite recursion on self-dependencies
             if getattr(self, '_none_checking', False):
                 # self-dependency - either this node receives a None

Cython/Compiler/FlowControl.py

@@ -711,9 +711,7 @@ class CreateControlFlowGraph(CythonTransform):
         self.in_inplace_assignment = True
         self.visitchildren(node)
         self.in_inplace_assignment = False
-        expr_node = node.create_binop_node()
-        expr_node.type = expr_node.infer_type(self.env)
-        self.mark_assignment(node.lhs, expr_node)
+        self.mark_assignment(node.lhs, node.create_binop_node())
         return node
 
     def visit_DelStatNode(self, node):