Fix VOLUME_LABEL when BRANCH contains non-alpha
characters, in particular '-' and '.'.

Submitted by:	des
Tested by:	des
MFC after:	3 days
X-MFC-10.1:	yes
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274095 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f