allow http assets that don't have css extension
allow http assets that don't have css extension

closes #437
sportradar/assetic,matthiasmullie/assetic,matthiasmullie/assetic,fredemmott/assetic,webmozart/assetic,mubassirhayat/assetic,webmozart/assetic,matthiasmullie/assetic,sportradar/assetic,shandy05/assetic,Sgoettschkes/assetic,kriswallsmith/assetic,Sgoettschkes/assetic,Sgoettschkes/assetic,renaatdemuynck/assetic,renaatdemuynck/assetic,mubassirhayat/assetic,Sgoettschkes/assetic,renaatdemuynck/assetic,kriswallsmith/assetic,webmozart/assetic,lenar/assetic,lellimecnar/assetic,lellimecnar/assetic,renaatdemuynck/assetic,matthiasmullie/assetic,lellimecnar/assetic,lenar/assetic,shandy05/assetic,sportradar/assetic,kriswallsmith/assetic,shandy05/assetic,fredemmott/assetic,kriswallsmith/assetic,mubassirhayat/assetic,lenar/assetic,lellimecnar/assetic,fredemmott/assetic,shandy05/assetic,lenar/assetic