Ensure sequences are properly read-locked in for-loops

Cython/Compiler/ExprNodes.py

@@ -2837,6 +2837,17 @@ class IteratorNode(ExprNode):
             return sequence_type
         return py_object_type
 
+    def ensure_rhs_locked(self, env, is_dereferenced = False):
+        self.sequence.ensure_rhs_locked(env, is_dereferenced = True)
+        if not self.tracked_state:
+            self.get_tracked_state(env)
+        if is_dereferenced and self.tracked_state:
+            if not self.is_rhs_locked(env):
+                if self.is_checklock():
+                    error(self.pos, "This expression is not correctly locked (read lock needed)")
+                elif self.is_autolock():
+                    self.set_autorlock(env)
+
     def analyse_cpp_types(self, env):
         sequence_type = self.sequence.type
         if sequence_type.is_ptr: