fix NPE on showProgressHandler (fix #8317)
fix NPE on showProgressHandler (fix #8317)

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