This fixes the issue with recursive ServerCommandEx in old engine (pre-Nuclear Dawn). The issue was that if ServerCommandEx is called recursively, sm_conhook_start and sm_conhook_stop will be added to the console buffer again. When that happens, it will set g_OriginalSpewOutputFunc to SourcemodSpewOutputFunc because the earlier call set the spew func to SourcemodSpewOutputFunc, and then when a line is printed, SourcemodSpewOutputFunc will call SourcemodSpewOutputFunc indefinitely until the stack overflows (in debug) or you get bored (in release). This patch fixes that by checking if we're already catching spew before adding sm_conhook_start/stop again.