fix #3569: concurrent modification when filtering caches on map
fix #3569: concurrent modification when filtering caches on map

xiaoyanit/cgeo,samueltardieu/cgeo,kumy/cgeo,lewurm/cgeo,pstorch/cgeo,madankb/cgeo,brok85/cgeo,cgeo/cgeo,tobiasge/cgeo,samueltardieu/cgeo,ThibaultR/cgeo,Huertix/cgeo,Huertix/cgeo,yummy222/cgeo,cgeo/cgeo,lewurm/cgeo,mucek4/cgeo,vishwakulkarni/cgeo,schwabe/cgeo,vishwakulkarni/cgeo,matej116/cgeo,marco-dev/c-geo-opensource,xiaoyanit/cgeo,KublaikhanGeek/cgeo,rsudev/c-geo-opensource,kumy/cgeo,superspindel/cgeo,mucek4/cgeo,auricgoldfinger/cgeo,auricgoldfinger/cgeo,kumy/cgeo,S-Bartfast/cgeo,pstorch/cgeo,Bananeweizen/cgeo,SammysHP/cgeo,schwabe/cgeo,ThibaultR/cgeo,rsudev/c-geo-opensource,cgeo/cgeo,samueltardieu/cgeo,Bananeweizen/cgeo,S-Bartfast/cgeo,SammysHP/cgeo,matej116/cgeo,S-Bartfast/cgeo,KublaikhanGeek/cgeo,matej116/cgeo,Huertix/cgeo,pstorch/cgeo,yummy222/cgeo,madankb/cgeo,lewurm/cgeo,Bananeweizen/cgeo,ThibaultR/cgeo,yummy222/cgeo,SammysHP/cgeo,tobiasge/cgeo,auricgoldfinger/cgeo,xiaoyanit/cgeo,mucek4/cgeo,superspindel/cgeo,vishwakulkarni/cgeo,cgeo/cgeo,marco-dev/c-geo-opensource,brok85/cgeo,rsudev/c-geo-opensource,schwabe/cgeo,brok85/cgeo,marco-dev/c-geo-opensource,KublaikhanGeek/cgeo,madankb/cgeo,tobiasge/cgeo,superspindel/cgeo,schwabe/cgeo