Martin Storsjö authored Dec 21, 2017 and Jean-Baptiste Kempf committed Dec 27, 2017

Without this, when reconfiguring, BUILD_FILEVERSION will end up with
a trailing comma with no revision number, which means that
src/versioninfo.rc will have a syntax error on build.

To reproduce/understand, download the plain gcrypt tarball;
configure contains a line like this:
    BUILD_FILEVERSION="${BUILD_FILEVERSION}45409"
After running configure, src/versioninfo.rc contains
"FILEVERSION 1,7,8,45409".

If running autoreconfigure with no enclosing git repo anywhere,
the same line in configure will end up as this:
    BUILD_FILEVERSION="${BUILD_FILEVERSION}"
After configuring, src/versioninfo.rc will now contain
"FILEVERSION 1,7,8,", which results in syntax errors.

As long as an enclosing git repo is available somewhere (if
the surrounding vlc tree contains a .git directory), this isn't
an issue though.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>