gui/infoviewer: check for time being set
infoviewer: only show remaining time if time is set

taken from martiis-neutrino-mp; based on code by seife;
contains an addition to ab42e7f032514b22c069fa523a40ae7c02e55ec0
Merge remote-tracking branch 'cool-next-cc/next-cc'

Conflicts:
	src/gui/infoviewer.cpp