Avoid Watchdog thread clobbering m_isExpired flag after callback (#1527)

wpilibc/src/main/native/cpp/Watchdog.cpp

@@ -58,10 +58,15 @@ void Watchdog::Thread::Main() {
                         << "s\n";
           }
         }
+
+        // Set expiration flag before calling the callback so any manipulation
+        // of the flag in the callback (e.g., calling Disable()) isn't
+        // clobbered.
+        watchdog->m_isExpired = true;
+
         lock.unlock();
         watchdog->m_callback();
         lock.lock();
-        watchdog->m_isExpired = true;
       }
       // Otherwise, a Watchdog removed itself from the queue (it notifies the
       // scheduler of this) or a spurious wakeup occurred, so just rewait with