plugin-volume: Handle errors when trying to determine the next card
plugin-volume: Handle errors when trying to determine the next card

Handle the error and warn about it.

lxde/lxqt-panel,stefonarch/lxqt-panel,pmattern/lxqt-panel,stefonarch/lxqt-panel,stefonarch/lxqt-panel,pmattern/lxqt-panel,lxde/lxqt-panel