bug(a.keygrabber): Stop timer when stopping keygrabber

When stopping a keygrabber with a timeout manually or through the stop
key, the timer would continue and call the stop callback again some time
later.

The error message in `gears.timer:stop` is removed, since there actually
is no harm in just returning immediately. And the timer implementation
itself calls `:stop` in certain places without checking for `.started`,
which lead to a situation where the internal call to `stop` triggered
the error message.

Signed-off-by: Lucas Schwiderski <lucas@lschwiderski.de>

lib/awful/keygrabber.lua

@@ -474,12 +474,20 @@ function keygrabber:start()
 end
 
 --- Stop the keygrabber.
+--
+-- Also stops any `timeout`.
+--
 -- @method stop
 -- @emits stopped
 -- @emits property::current_instance
 function keygrabber:stop(_stop_key, _stop_mods) -- (at)function disables ldoc params
     keygrab.stop(self.grabber)
 
+    local timer = self._private.timer
+    if timer and timer.started then
+        timer:stop()
+    end
+
     if self.stop_callback then
         self.stop_callback(
             self.current_instance, _stop_key, _stop_mods, self.sequence

lib/gears/timer.lua

@@ -99,11 +99,13 @@ function timer:start()
 end
 
 --- Stop the timer.
+--
+-- Does nothing if the timer isn't running.
+--
 -- @method stop
 -- @emits stop
 function timer:stop()
     if self.data.source_id == nil then
-        gdebug.print_error(traceback("timer not started"))
         return
     end
     glib.source_remove(self.data.source_id)