Fixes #1405: No error message for invalid syntax in period_archives.html
Fixes #1405: No error message for invalid syntax in period_archives.html

jimperio/pelican,catdog2/pelican,eevee/pelican,gymglish/pelican,alexras/pelican,joetboole/pelican,Summonee/pelican,levanhien8/pelican,avaris/pelican,Rogdham/pelican,lazycoder-ru/pelican,karlcow/pelican,getpelican/pelican,jimperio/pelican,JeremyMorgan/pelican,iurisilvio/pelican,florianjacob/pelican,eevee/pelican,farseerfc/pelican,eevee/pelican,TC01/pelican,simonjj/pelican,rbarraud/pelican,Scheirle/pelican,ls2uper/pelican,51itclub/pelican,51itclub/pelican,avaris/pelican,deved69/pelican-1,iKevinY/pelican,douglaskastle/pelican,zackw/pelican,UdeskDeveloper/pelican,TC01/pelican,treyhunner/pelican,deved69/pelican-1,HyperGroups/pelican,douglaskastle/pelican,koobs/pelican,abrahamvarricatt/pelican,deanishe/pelican,simonjj/pelican,rbarraud/pelican,florianjacob/pelican,alexras/pelican,karlcow/pelican,deanishe/pelican,lucasplus/pelican,UdeskDeveloper/pelican,ehashman/pelican,number5/pelican,talha131/pelican,Rogdham/pelican,Summonee/pelican,gymglish/pelican,TC01/pelican,jimperio/pelican,simonjj/pelican,JeremyMorgan/pelican,gymglish/pelican,kennethlyn/pelican,deanishe/pelican,jvehent/pelican,levanhien8/pelican,Polyconseil/pelican,douglaskastle/pelican,ehashman/pelican,ls2uper/pelican,JeremyMorgan/pelican,treyhunner/pelican,GiovanniMoretti/pelican,kennethlyn/pelican,ehashman/pelican,lucasplus/pelican,jvehent/pelican,iurisilvio/pelican,catdog2/pelican,treyhunner/pelican,koobs/pelican,51itclub/pelican,Scheirle/pelican,catdog2/pelican,ingwinlu/pelican,Summonee/pelican,farseerfc/pelican,iurisilvio/pelican,alexras/pelican,lazycoder-ru/pelican,koobs/pelican,HyperGroups/pelican,Polyconseil/pelican,kennethlyn/pelican,zackw/pelican,jvehent/pelican,lazycoder-ru/pelican,UdeskDeveloper/pelican,karlcow/pelican,levanhien8/pelican,joetboole/pelican,getpelican/pelican,Rogdham/pelican,HyperGroups/pelican,garbas/pelican,abrahamvarricatt/pelican,talha131/pelican,iKevinY/pelican,deved69/pelican-1,rbarraud/pelican,ingwinlu/pelican,Scheirle/pelican,florianjacob/pelican,garbas/pelican,GiovanniMoretti/pelican,lucasplus/pelican,joetboole/pelican,garbas/pelican,ls2uper/pelican,number5/pelican,zackw/pelican,abrahamvarricatt/pelican,GiovanniMoretti/pelican,number5/pelican