git-version-gen: Fail on UNKNOWN version

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>

build-aux/git-version-gen

@@ -160,6 +160,14 @@ else
     fi
 fi
 
+if test "$v" = "UNKNOWN"
+then
+  echo "$0: ERROR: Can't find valid version. Please use valid git repository," \
+    "released tarball or version tagged archive" 1>&2
+
+  exit 1
+fi
+
 v=`echo "$v" |sed 's/^v//'`
 
 # Don't declare a version "dirty" merely because a time stamp has changed.