ids-functions.pl: Merge same named rulefiles during extract.

ids-functions.pl: Merge same named rulefiles during extract.

In case a rulestarball contains several same-named rulefiles
they have been overwritten each time and so only contained the content
from the last extracted one.

Now the content of those files will be merged by appending the content
to the first extracted one for each time.

Fixes #12792.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>