Fix test-leak-client.lua under LuaCov

Both the test runner and the wibox use gears.timer.delayed_call(). The test
runner uses this to call steps and the wibox uses it to trigger redraws. When
running under LuaCov, the Lua code becomes slow enough that the wibox didn't
redraw yet when the leak check is run. This causes the check to fail, because
the client is still referenced by the tasklist and thus cannot be garbage
collected.

Fix this by waiting one more iteration before running the leak check.

Signed-off-by: Uli Schlachter <psychon@znc.in>

tests/test-leak-client.lua

@@ -46,6 +46,7 @@ collectgarbage("stop")
 -- The first iteration starts xterm, the second keeps a weak reference to it and
 -- closes it and the last one checks that the client object is GC'able.
 local objs = nil
+local second_call = false
 local steps = {
     function(count)
         if count == 1 then
@@ -56,6 +57,10 @@ local steps = {
                 objs = setmetatable({ c }, { __mode = "v" })
                 c:kill()
             end
+        elseif not second_call then
+            -- Wait for one iteration so that gears.timer handles other delayed
+            -- calls (= the tasklist updates)
+            second_call = true
         else
             assert(#objs == 1)