testbase: Always do a final screenshot, even if one is already pending
testbase: Always do a final screenshot, even if one is already pending

Otherwise we might never exit.

chergert/gnome-continuous,vrutkovs/vrutkovs.github.io,vrutkovs/vrutkovs.github.io,vrutkovs/vrutkovs.github.io,chergert/gnome-continuous,chergert/gnome-continuous