[OpenSIPS-Devel] [OpenSIPS/opensips] dfb9b4: [dialog] fix dropping empty string dlg vals

[Bogdan Andrei IANCU]

  Branch: refs/heads/3.3
  Home:   https://github.com/OpenSIPS/opensips
  Commit: dfb9b4f8a5846d55302563bacfbd988d000d8a3d
      https://github.com/OpenSIPS/opensips/commit/dfb9b4f8a5846d55302563bacfbd988d000d8a3d
  Author: Bogdan-Andrei Iancu <bogdan at opensips.org>
  Date:   2023-06-27 (Tue, 27 Jun 2023)

  Changed paths:
    M modules/dialog/dlg_db_handler.c

  Log Message:
  -----------
  [dialog] fix dropping empty string dlg vals

Upon DB recovery (after an OpenSIPS restart) do not drop emtpy string dlg vals - as we do allow creation of such vals via cfg and api and have them saved to DB, it makes all the sense to also restore them
This triggers some startup warnings when using in-dialog re-INVITE probing.
Closes #3108

(cherry picked from commit e24668131bcd828214c4fb9bccb208e9483a2a4e)