[openSUSE/obs-build] 451a4f: Add a test to check if we know the specified files...

22 Dec 2020

      Branch: refs/heads/master
  Home:   https://github.com/openSUSE/obs-build
  Commit: 451a4fb29565e4e29e0c5b18f17a972ee24fecfd
      https://github.com/openSUSE/obs-build/commit/451a4fb29565e4e29e0c5b18f17a972...
  Author: Michael Schroeder <mls@suse.de>
  Date:   2020-12-22 (Tue, 22 Dec 2020)

  Changed paths:
    M build-vm

  Log Message:
  -----------
  Add a test to check if we know the specified filesystem

For some reason bash terminates the function if the variable
name is bad in a ${!var} expansion. So make sure that var
is known to return a valid error.