krb5: fix uninitialized variable warning

On some targets clang erroniously detects an uninitialized variable.
Backport the fix from upstream.

Signed-off-by: Daniel McGregor <daniel.mcgregor@vecima.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
(cherry picked from commit 5da9408672d3929d2f71d0b15a8e06043c5a1109)
Signed-off-by: Armin Kuster <akuster808@gmail.com>