[KPhotoAlbum] Compiler warnings

[Robert Krawitz]

I'm getting a flood of warnings:

In file included from /home/rlk/sandbox/kphotoalbum/BackgroundTaskManager/JobManager.cpp:21:0:
/home/rlk/sandbox/kphotoalbum/ImageManager/AsyncLoader.h:57:18: warning: ‘virtual void ImageManager::AsyncLoader::customEvent(QEvent*)’ can be marked override [-Wsuggest-override]
     virtual void customEvent( QEvent* ev );

Using g++ 7.3.1.

-- 
Robert Krawitz                                     <rlk at alum.mit.edu>

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