monitor: Fix command completion vs. boolean switches

We now have to move forward to the next argument type via next_arg_type.
This patch fixes completion for 'eject' and maybe also other commands.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

monitor.c

@@ -3918,7 +3918,7 @@ static void monitor_find_completion(const char *cmdline)
         }
         str = args[nb_args - 1];
         if (*ptype == '-' && ptype[1] != '\0') {
-            ptype += 2;
+            ptype = next_arg_type(ptype);
         }
         switch(*ptype) {
         case 'F':