fix #3721: NPE in Geocache.hashCode()
fix #3721: NPE in Geocache.hashCode()

Also, hash codes must be equal when the objects compare equal. Since
equality compares only geocodes, the hash codes must also only take
geocodes into consideration.

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