- sanitized the 'frozen level' code.

This had two different flags that were checked totally inconsistently, and one was not even saved.
Moved everything into a few subfunctions so that these checks do not have to be scattered all over the code.

src/b_bot.cpp

@@ -49,6 +49,7 @@
 #include "d_player.h"
 #include "w_wad.h"
 #include "vm.h"
+#include "g_levellocals.h"
 
 IMPLEMENT_CLASS(DBot, false, true)
 
@@ -137,7 +138,7 @@ void DBot::Tick ()
 {
 	Super::Tick ();
 
-	if (player->mo == nullptr || bglobal.freeze)
+	if (player->mo == nullptr || Level->isFrozen())
 	{
 		return;
 	}