sync: removed redundant error checks
sync: removed redundant error checks

We don't need to check mpd_async_get_error() right before calling
another async function.  All async functions perform error checking
already.

psych0tik/libmpdclient2,yusiwen/libmpdclient,sl0th/libmpdclient,jagleeso/libmpdclient,psych0tik/libmpdclient2,jwise/libmpdclient,cmende/libmpdclient,yusiwen/libmpdclient,jagleeso/libmpdclient,sl0th/libmpdclient,cmende/libmpdclient,jwise/libmpdclient,jwise/libmpdclient,yusiwen/libmpdclient,jagleeso/libmpdclient,sl0th/libmpdclient,cmende/libmpdclient