Steps to reproduce:
1. Import some layer - set Git revision to master.
2. Go to edit layer and change Git revision to krogoth.
3. In that layer I didn't have master branch (only krogoth) so my build failed with:

WARNING localhostbecontroller: shellcmd error command: git fetch --all && git reset --hard "origin/master"
From host:project
* [new branch]      krogoth    -> origin/krogoth
fatal: ambiguous argument 'origin/master': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

I checked in database what happened and I found out, that my layer in orm_layer_version table has branch set as master and commit set as krogoth. 
After I changed branch to krogoth in the database everything works fine.