Fixed problem with .less files being sometimes incorrectly cached

I do not why this is happening exactly, but while deving my app I get not correctly compiled css files.

This files have not even empty any serialized content in them, but something very cryptic.
I think this results from not until the end rendered views or something, but I am not completly sure about it.

I know how to fix this problem and did it with this PR.

Regards
func0der