added fix for unit debugg crash

src/Unit.cpp

@@ -328,7 +328,9 @@ void Unit::ability(sc2::AbilityID ability, const Unit& target) const
 Unit Unit::getTarget() const
 {
     BOT_ASSERT(isValid(), "Unit is not valid");
-    BOT_ASSERT(hasTarget(), "Unit has no target");
+    if (!hasTarget()){
+	return NULL
+    }
 
     // if unit has order, check tag of target of first order
     if(getUnitPtr()->orders.size() > 0){