fix #9459: install safeguard in case of null-viewport
fix #9459: install safeguard in case of null-viewport

cgeo/cgeo,S-Bartfast/cgeo,rsudev/c-geo-opensource,tobiasge/cgeo,auricgoldfinger/cgeo,matej116/cgeo,auricgoldfinger/cgeo,rsudev/c-geo-opensource,auricgoldfinger/cgeo,matej116/cgeo,cgeo/cgeo,tobiasge/cgeo,cgeo/cgeo,rsudev/c-geo-opensource,cgeo/cgeo,S-Bartfast/cgeo,matej116/cgeo,S-Bartfast/cgeo,tobiasge/cgeo