Vehicle.cc: avoid weak_ptr::expired() & weak_ptr::lock() call combination

- if used multi-threaded: avoids a race condition
- if not: reduces amount of atomic ops

src/Vehicle/Vehicle.cc

@@ -2661,11 +2661,10 @@ void Vehicle::_sendMavCommandWorker(bool commandInt, bool requestMessage, bool s
         return;
     }
 
-    WeakLinkInterfacePtr weakLink = vehicleLinkManager()->primaryLink();
+    SharedLinkInterfacePtr sharedLink = vehicleLinkManager()->primaryLink().lock();
 
-    if (!weakLink.expired()) {
+    if (sharedLink) {
         MavCommandListEntry_t   entry;
-        SharedLinkInterfacePtr  sharedLink = weakLink.lock();
 
         entry.useCommandInt     = commandInt;
         entry.targetCompId      = targetCompId;