cmdline: Redraw the cmdline after processing events

vim-patch:7.4.1603

TODO(bfredl): if we allow events in HITRETURN and ASKMORE states,
we need to add the necessary redraws as well.

src/nvim/ex_getln.c

@@ -359,6 +359,7 @@ static int command_line_execute(VimState *state, int key)
 
   if (s->c == K_EVENT) {
     queue_process_events(loop.events);
+    redrawcmdline();
     return 1;
   }