make lastUsedImageDir static to prevent a crash

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Merge branch 'master' of https://github.com/torvalds/subsurface
Merge branch 'master' of https://github.com/torvalds/subsurface
Merge branch 'master' of https://github.com/torvalds/subsurface
Merge branch 'master' of https://github.com/torvalds/subsurface
Merge branch 'master' of https://github.com/torvalds/subsurface
Merge branch 'oneplannertable' of https://github.com/atdotde/subsurface
Merge branch 'oneplannertable' of https://github.com/atdotde/subsurface into oneplannertable
Merge branch 'oneplannertable' of https://github.com/atdotde/subsurface into oneplannertable
Merge branch 'oneplannertable' of https://github.com/atdotde/subsurface into oneplannertable
with accessors, still not working

Signed-off-by: Robert C. Helling <helling@atdotde.de>
morgen mehr

Signed-off-by: Robert C. Helling <helling@atdotde.de>