1) remove Lifeforce and Deathgrip from AI decks

2) fix potential NullPointerException in canPlayAI for Lifeforce and Deathgrip

res/cardsfolder/deathgrip.txt

@@ -2,6 +2,7 @@ Name:Deathgrip
 ManaCost:B B
 Types:Enchantment
 Text:B B: Counter target green spell.
+SVar:RemAIDeck:True
 SVar:Rarity:Uncommon
 SVar:Picture:http://www.wizards.com/global/images/magic/general/deathgrip.jpg
 End

res/cardsfolder/lifeforce.txt

@@ -2,6 +2,7 @@ Name:Lifeforce
 ManaCost:G G
 Types:Enchantment
 Text:G G: Counter target black spell.
+SVar:RemAIDeck:True
 SVar:Rarity:Uncommon
 SVar:Picture:http://www.wizards.com/global/images/magic/general/lifeforce.jpg
 End

src/forge/CardFactory.java

@@ -11868,6 +11868,9 @@ public class CardFactory implements NewConstants {
         		@Override
         		public boolean canPlayAI() {
         			System.out.println("AI is pondering using "+cardName);
+        			if(AllZone.Stack.size() == 0){
+        				return false;
+        			}
         			SpellAbility sa = AllZone.Stack.peek();
         			return canPlay() && sa.getSourceCard().getController().equals(AllZone.HumanPlayer);
         		}
@@ -11905,6 +11908,9 @@ public class CardFactory implements NewConstants {
         		@Override
         		public boolean canPlayAI() {
         			System.out.println("AI is pondering using "+cardName);
+        			if(AllZone.Stack.size() == 0){
+        				return false;
+        			}
         			SpellAbility sa = AllZone.Stack.peek();
         			return canPlay() && sa.getSourceCard().getController().equals(AllZone.HumanPlayer);
         		}