gnomebase.bbclass: return the whole version for tarball directory if it is a number

E.g. if version is '43' without any dots, existing code would return ''.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit 38c15322)
Signed-off-by: Steve Sakoman <steve@sakoman.com>