log error on invalid slug - only when setting the value from frontmatter
log error on invalid slug - only when setting the value from frontmatter

sylvestrelucia/grav,getgrav/grav,dimayakovlev/grav,Sommerregen/grav,gigago/grav,sylvestrelucia/grav,shortsofia/testesitegrav.github.io,userfrosting/learn,sylvestrelucia/grav,JamesPan/gravbox,JamesPan/gravbox,notklaatu/grav,stell/grav,JamesPan/gravbox,joeyhenricks/a-broke-vegan,userfrosting/learn,webuxr/iamrs,userfrosting/learn,tomzx/blog.tomrochette.com,JamesPan/gravbox,Vivalldi/grav,userfrosting/learn,Vivalldi/grav,joeyhenricks/a-broke-vegan,tomzx/blog.tomrochette.com,tomzx/blog.tomrochette.com,tomzx/blog.tomrochette.com,ccardinaux/grav-test,notklaatu/grav,getgrav/grav,sylvestrelucia/grav,toovy/grav,toovy/grav,dimayakovlev/grav