(Db_traverse_tag_find) fix a rare segfault

found accidently

could be triggered by the following (calling enough times either
requires() or provides() while traversing rpm db) which resulting in
an "Invalid read of size 8":

use URPM;
my $db = URPM::DB::open()->traverse_tag_find('whatprovides', 'kernel',
sub {
    my ($p) = @_;
    warn $p->requires, $p->requires, $p->requires, $p->requires, $p->requires,
    $p->requires, $p->requires, $p->requires, $p->requires, $p->requires, $p->requires,
    $p->requires, $p->requires, $p->requires, $p->requires, $p->requires, $p->requires;
    return 1;
});

bug introduced in commit r4947 on June 14 2012:
"(_run_cb_while_traversing) introduce this helper"

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index c7d4425..95291f5 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,5 @@
+- fix a rare segfault
+
 Version 4.19 - 2 December 2012
 
 - kill pkg->disttag (unused, introduced for rpm5 prior to the fork)