Fix screen freeze (fixes #94)

Fixes screen freeze after setting adjustement mode to width and changing the workspace. Problem occurs on multi monitor setup, when another monitor with different ppi is returned by gdk_display_get_monitor_at_window than the one the (now hidden) window is on (probably just the leftmost monitor). Adding adjust_view to zathura_update_view_ppi fixes the issue, because the view gets adjusted to the ppi change.

This should probably fix #94, but maybe just partially. Tested on ArchLinux with dwm.