Fix warning about pytaken_msg maybe being uninitialized

[sloretz]

Seen in https://ci.ros2.org/job/nightly_linux_release/1525/gcc/new/

This initializes pytaken_msg with NULL, and changes the check that pytaken_msg is not NULL to cover both raw and non-raw cases.

[sloretz]

CI (testing just rclpy)

• Linux
• Linux-aarch64
• macOS
• Windows

[sloretz]

CI windows only shows these test failures which are clearly unrelated to this PR

    projectroot.test_timer
    rclpy.src.ros2.rclpy.rclpy.test.test_timer.test_zero_callback[0.01]
    rclpy.src.ros2.rclpy.rclpy.test.test_timer.test_number_callbacks[0.01]

But console output shows

19: ..\..\src\ros2\rclpy\rclpy\test\test_node.py ........................... [ 46%]
19: F..............................                                          [100%]
19: 
19: ================================== FAILURES ===================================
19: _________________ TestNodeAllowUndeclaredParameters.test_take _________________
19: 
19: self = <test.test_node.TestNodeAllowUndeclaredParameters testMethod=test_take>
19: 
19:     def test_take(self):
19:         basic_types_pub = self.node.create_publisher(BasicTypes, 'take_test', 1)
19:         sub = self.node.create_subscription(
19:             BasicTypes,
19:             'take_test',
19:             self.dummy_cb,
19:             1)
19:         basic_types_msg = BasicTypes()
19:         basic_types_pub.publish(basic_types_msg)
19:         cycle_count = 0
19:         while cycle_count < 5:
19:             with sub.handle as capsule:
19:                 result = _rclpy.rclpy_take(capsule, sub.msg_type, False)
19:             if result is not None:
19:                 msg, info = result
19: >               self.assertNotEqual(0, info['source_timestamp'])
19: E               TypeError: 'NoneType' object is not subscriptable
19: 
19: ..\..\src\ros2\rclpy\rclpy\test\test_node.py:157: TypeError
19: - generated xml file: C:\ci\ws\build\rclpy\test_results\rclpy\test_node.xunit.xml -
19: =========================== short test summary info ===========================
19: FAILED ..\..\src\ros2\rclpy\rclpy\test\test_node.py::TestNodeAllowUndeclaredParameters::test_take
19: ======================== 1 failed, 57 passed in 0.95s =========================
19: -- run_test.py: return code 1
19: -- run_test.py: verify result file 'C:/ci/ws/build/rclpy/test_results/rclpy/test_node.xunit.xml'
19/45 Test #19: test_node .........................***Failed    1.81 sec
test 20

Which may be related, and wasn't captured in the test results. Investigating.

[sloretz]

Which may be related, and wasn't captured in the test results. Investigating.

Ok, I think I understand what happened here. The test got re-ran because CI uses --retest-until-pass 2 and the second test passed. The test is flaky and passed the second time. This comes down to rclpy_take() returning (None, None) when take fails since #550 (@hidmic FYI) which was added to fix #542 crashing in this case, but the original behavior is that the code used to return just None. This happens when the subscription wakes the wait set, but the middleware says there is no message.

Anyways, this PR is good as is. I'll open a separate PR to make rclpy_take return just None like it used to. Edit: changed my mind about how I'd like to fix this.