add wait for images loading
add wait for images loading

Images loading was non-blocking leading to incorrect
progress report

Fixes #7395

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