Fix in pakfire functions.sh

Fix in pakfire functions.sh

The if statement in line 89 and 99 are useless with the -e
conditional expression because it returns true if the path ist a
regular file or a directory.
So "/etc/init.d/ " returns true and "/etc/init.d/avahi" return also true,
but the statement should return only true if we have a regular file.
So -f if the right conditional expression, and we only try to execute
the init script if the path "/etc/init.d/${1}" points to a regular file.

Signed-off-by: Jonatan Schlag <jonatan.schlag@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>