Input: Don't re-run the slot creation check on key sets

Make sure we always create the storage table when we add its reference
to the MTSlots list instead.

(The reasoning being we only add the reference once, and it's the first
thing we do, and we kinda need the storage to be created to get its
reference anyway; while we may set multiple keys per frame).

frontend/device/input.lua

@@ -815,7 +815,7 @@ function Input:handleTouchEvLegacy(ev)
     -- In those devices the 'handleTouchEv' function doesn't work as expected. Use this function instead.
     if ev.type == C.EV_ABS then
         if #self.MTSlots == 0 then
-            table.insert(self.MTSlots, self:getMtSlot(self.cur_slot))
+            self:addSlot(self.cur_slot)
         end
         if ev.code == C.ABS_X then
             self:setCurrentMtSlot("x", ev.value)
@@ -989,8 +989,6 @@ function Input:initMtSlot(slot)
 end
 
 function Input:setMtSlot(slot, key, val)
-    self:initMtSlot(slot)
-
     self.ev_slots[slot][key] = val
 end