various minor fixes

common/buildcraft/core/robots/AIRobotCraftWorkbench.java

@@ -66,6 +66,11 @@ public class AIRobotCraftWorkbench extends AIRobotCraftGeneric {
 
 	@Override
 	public void update() {
+		if (recipe == null) {
+			// loading error
+			terminate();
+			return;
+		}
 
 		// [1] look for a crafting order
 		// -- if none, clear temporary item blacklist and sleep

common/buildcraft/core/robots/AIRobotGotoRandomGroundBlock.java

@@ -46,8 +46,12 @@ public class AIRobotGotoRandomGroundBlock extends AIRobot {
 		} else {
 			if (!pathFindingJob.isAlive()) {
 				LinkedList<BlockIndex> path = pathFinding.getResult();
-				path.removeLast();
-				startDelegateAI(new AIRobotGotoBlock(robot, path));
+				if (path.size() == 0) {
+					terminate();
+				} else {
+					path.removeLast();
+					startDelegateAI(new AIRobotGotoBlock(robot, path));
+				}
 			}
 		}
 	}

common/buildcraft/core/robots/AIRobotLoad.java

@@ -49,6 +49,12 @@ public class AIRobotLoad extends AIRobot {
 
 	@Override
 	public void update() {
+		if (filter == null) {
+			// loading error
+			terminate();
+			return;
+		}
+
 		waitedCycles++;
 
 		if (waitedCycles > 40) {

common/buildcraft/core/robots/DockingStation.java

@@ -100,7 +100,7 @@ public class DockingStation implements IDockingStation {
 	}
 
 	public boolean takeAsMain(EntityRobotBase robot) {
-		if (robotTaking == null) {
+		if (robotTakingId == EntityRobotBase.NULL_ROBOT_ID) {
 			linkIsMain = true;
 			robotTaking = robot;
 			robotTakingId = robot.getRobotId();
@@ -111,7 +111,7 @@ public class DockingStation implements IDockingStation {
 
 			return true;
 		} else {
-			return false;
+			return robotTakingId == robot.getRobotId();
 		}
 	}