Filter out stylesheets without that do not exist when loading a project. Fixes #133.
Filter out stylesheets without that do not exist when loading a project. Fixes #133.

Zhao-Qi/tilemill,fxtentacle/tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,tizzybec/tilemill,tilemill-project/tilemill,florianf/tileoven,tizzybec/tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,mbrukman/tilemill,paulovieira/tilemill-clima,MappingKat/tilemill,isaacs/tilemill,nyimbi/tilemill,nyimbi/tilemill,tilemill-project/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,makinacorpus/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,nyimbi/tilemill,isaacs/tilemill,MappingKat/tilemill,fxtentacle/tilemill,tizzybec/tilemill,makinacorpus/tilemill,florianf/tileoven,paulovieira/tilemill-clima,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill,MappingKat/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,Zhao-Qi/tilemill,florianf/tileoven,tizzybec/tilemill,isaacs/tilemill,nyimbi/tilemill,MappingKat/tilemill,tilemill-project/tilemill,Zhao-Qi/tilemill,fxtentacle/tilemill,mbrukman/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,mbrukman/tilemill,mbrukman/tilemill,fxtentacle/tilemill,fxtentacle/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,nyimbi/tilemill,MappingKat/tilemill