Merge pull request #5834 from SJuliez/5769-id-overlap

#5769: Possibly fix ID overlap when reinforcing from MUL

megamek/src/megamek/common/Game.java

@@ -1189,7 +1189,7 @@ public synchronized void addEntity(Entity entity, boolean genEvent) {
         }
         // Add this Entity, ensuring that its id is unique
         int id = entity.getId();
-        if (inGameObjects.containsKey(id)) {
+        if (isIdUsed(id)) {
             id = getNextEntityId();
             entity.setId(id);
         }
@@ -1216,6 +1216,13 @@ && getOptions().booleanOption(OptionsConstants.RPG_CONDITIONAL_EJECTION)) {
         }
     }
 
+    /**
+     * @return true if the given ID is in use among active and dead units
+     */
+    private boolean isIdUsed(int id) {
+        return inGameObjects.containsKey(id) || isOutOfGame(id);
+    }
+
     public void setEntity(int id, Entity entity) {
         setEntity(id, entity, null);
     }