Disable multi-volume feature at least for gbak -c stdin

[basid-irk]

Currently:

 gbak -c stdin

unconditionaly request new volume of backup on unexpected "end of file". This prompt are inaccessible if gbak work in background (nohub|& or start/b). On Linux impossible gracefull terminate gbak proccess in that state - only via "kill bus" (kill -9).