More AI fixes/improvements:

- AI characters can refuel the reactor when needed.
- AIObjectiveContainItem.CanBeCompleted returns true if the target item cannot be obtained or if the container cannot be reached.
- AI characters only weld leaks that are part of some submarine (i.e. not ruins).

Barotrauma/BarotraumaShared/Source/Characters/AI/Objectives/AIObjectiveFixLeaks.cs

@@ -106,6 +106,9 @@ namespace Barotrauma
                 if (gap.ConnectedWall == null) continue;
                 if (gap.ConnectedDoor != null || gap.Open <= 0.0f) continue;
 
+                //TODO: prevent the AI characters from fixing leaks in the enemy sub in sub-vs-sub missions if/when multiplayer bots are implemented
+                if (gap.Submarine == null) continue;
+
                 float gapPriority = GetGapFixPriority(gap);
 
                 int index = 0;