RGWListBucketMultiparts: init max_uploads/default_max with 0

CID 717377 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
 2. uninit_member: Non-static class member "max_uploads" is not initialized
    in this constructor nor in any functions that it calls.
 4. uninit_member: Non-static class member "default_max" is not initialized
    in this constructor nor in any functions that it calls.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
(cherry picked from commit b23a141d54ffb39958aba9da7f87544674fa0e50)