Fixed possible floating point exception in the beep thread. Instead of setting
'beep_bytes' to 0, now using new 'beep_control' variable (2 = run beep loop,
1 = request beep loop exit, 0 = beep loop has ended).


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12293 6c8e4198-a580-4521-a02f-c9ae86df1db9