Merge pull request #5813 from Sleet01/Fix_5705_NPE_computing_LAM_move…

…ment_envelope

Prevent NPE by using interface rather than Aero casting

megamek/src/megamek/client/ui/swing/MovementDisplay.java

@@ -4414,13 +4414,14 @@ public void computeAeroMovementEnvelope(Entity entity) {
         }
 
         // Increment the entity's delta-v then compute the movement envelope.
-        Aero ae = (Aero)entity;
+        // LAM and Aeros both implement this interface
+        IAero ae = (IAero) entity;
         int currentVelocity = ae.getCurrentVelocity();
         ae.setCurrentVelocity(cmd.getFinalVelocity());
 
         // Refresh the new velocity envelope on the map.
         try {
-            computeMovementEnvelope(ae);
+            computeMovementEnvelope(entity);
             updateMove();
         } catch (Exception e) {
             LogManager.getLogger().error("An error occured trying to compute the move envelope for an Aero.");