awful.tag.withcurrent: Try harder at finding a tag (FS#1196)

When a screen doesn't have any tags selected, then just tag the new client with
all of the screen's tags. That way, we don't lose clients.

Also, if we failed at coming up with tags for a client, don't completely untag
it. This means that it can keep its old tags if it had any.

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

lib/awful/tag.lua.in

@@ -530,7 +530,12 @@ function tag.withcurrent(c)
     if #tags == 0 then
         tags = tag.selectedlist(c.screen)
     end
-    c:tags(tags)
+    if #tags == 0 then
+        tags = tag.gettags(c.screen)
+    end
+    if #tags ~= 0 then
+        c:tags(tags)
+    end
 end
 
 local function attached_connect_signal_screen(screen, sig, func)