Directly nil check the first element of an array instead of the array's

size when we're only concerned with this single element.

frontend/device/wakeupmgr.lua

@@ -88,7 +88,7 @@ with anonymous functions.
 @treturn bool (true if one or more tasks were removed; false otherwise; nil if the task queue is empty).
 --]]
 function WakeupMgr:removeTasks(epoch, callback)
-    if #self._task_queue < 1 then return end
+    if #self._task_queue == 0 then return end
 
     local removed = false
     local reschedule = false
@@ -147,7 +147,7 @@ If necessary, the next upcoming task (if any) is scheduled on exit.
 @treturn bool (true if we were truly woken up by the scheduled wakeup; false otherwise; nil if there weren't any tasks scheduled).
 --]]
 function WakeupMgr:wakeupAction(proximity)
-    if #self._task_queue > 0 then
+    if self._task_queue[1] then
         local task = self._task_queue[1]
         if self:validateWakeupAlarmByProximity(task.epoch, proximity) then
             task.callback()

frontend/ui/uimanager.lua

@@ -1142,7 +1142,7 @@ end
 --]]
 
 function UIManager:getNextTaskTime()
-    if #self._task_queue > 0 then
+    if self._task_queue[1] then
         return self._task_queue[1].time - time:now()
     else
         return nil
@@ -1156,10 +1156,12 @@ function UIManager:_checkTasks()
     -- task.action may schedule other events
     self._task_queue_dirty = false
     while true do
-        if #self._task_queue == 0 then
+        if not self._task_queue[1] then
             -- Nothing to do!
             break
         end
+        -- FIXME: Err, the or makes no sense, UIManager:schedule should ensure time & action fields are sane?
+        --        Either check nothing, or check both time *and* action (which should *never* be nil, unless Greminls, c.f., #9112)
         local task_time = self._task_queue[1].time or 0
         if task_time <= self._now then
             -- remove from table