disallow attacking with disabled attacks via [do_command]

this fixes some rare cheats in mp.

(cherry-picked from commit 26b5ca5)

data/test/scenarios/feeding.cfg

@@ -30,6 +30,11 @@
     {VARIABLE victim_x $Killer.x}
     {VARIABLE_OP victim_x sub 1}
     {VARIABLE victim_y $Killer.y}
+    {VARIABLE Killer.attacks_left 1}
+
+    [unstore_unit]
+        variable=Killer
+    [/unstore_unit]
 
     {VARIABLE victim_side 3}
     {VARIABLE_OP victim_side sub $Killer.side|}
@@ -66,6 +71,7 @@
     {ASSERT ({VARIABLE_CONDITIONAL Killer.hitpoints equals $Killer_start_hp})}
 #enddef
 
+## TODO: the original feeding ability is implemented differently, maybe we should update this.
 {GENERIC_UNIT_TEST "feeding" (
     [event]
         id=ability_feeding_die

src/actions/attack.cpp

@@ -1403,6 +1403,11 @@ void attack::perform()
 		return;
 	}
 
+	if(a_.get_unit().attacks_left() <= 0) {
+		LOG_NG << "attack::perform(): not enough ap.\n";
+		return;
+	}
+
 	a_.get_unit().set_facing(a_.loc_.get_relative_dir(d_.loc_));
 	d_.get_unit().set_facing(d_.loc_.get_relative_dir(a_.loc_));
 
@@ -1424,6 +1429,11 @@ void attack::perform()
 	a_stats_ = &bc_->get_attacker_stats();
 	d_stats_ = &bc_->get_defender_stats();
 
+	if(a_stats_->disable) {
+		LOG_NG << "attack::perform(): tried to attack with a disabled attack.\n";
+		return;
+	}
+
 	if(a_stats_->weapon) {
 		a_.weap_id_ = a_stats_->weapon->id();
 	}