aout: reset volume to 1 on module unload
aout: reset volume to 1 on module unload

This fixes a corner case where the old volume of an output plugin using
software amplification would be wrongly applied to the next output
plugin instance (if that used "hardware" amplification).

vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.1,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc,jomanmuk/vlc-2.1,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,shyamalschandra/vlc,xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.2,krichter722/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.1,xkfz007/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,krichter722/vlc