bpo-33316: PyThread_release_lock always fails (GH-6541)

Use correct interpretation of return value from APIs.

Misc/NEWS.d/next/Windows/2018-04-20-03-24-07.bpo-33316.9IiJ8J.rst

+PyThread_release_lock always fails

Python/thread_nt.h

@@ -104,8 +104,9 @@ LeaveNonRecursiveMutex(PNRMUTEX mutex)
     if (PyMUTEX_LOCK(&mutex->cs))
         return FALSE;
     mutex->locked = 0;
-    result = PyCOND_SIGNAL(&mutex->cv);
-    result &= PyMUTEX_UNLOCK(&mutex->cs);
+    /* condvar APIs return 0 on success. We need to return TRUE on success. */
+    result = !PyCOND_SIGNAL(&mutex->cv);
+    PyMUTEX_UNLOCK(&mutex->cs);
     return result;
 }