file_dlg: prevent panic when nil event received during double click
file_dlg: prevent panic when nil event received during double click

cainiaocome/gxui,treejames/gxui,pombredanne/gxui,Drahoslav7/gxui,google/gxui,MeGaPk/gxui,ylong/gxui,henrikhodne/gxui,xinhuang327/gxui,jmptrader/gxui,Anaminus/gxui,CodyGuo/gxui,rnubel/gxui,insionng/gxui,mzgnr/gxui,abadojack/gxui,leelib/gxui,UIKit0/gxui