tdf#117480 fix crash in mailmerge

Catch exceptions and hide progress dialog.

b2d85f9207bc9bf7489d0a1fd9b35f062502639d
Reviewed-on: https://gerrit.libreoffice.org/65815Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>
Tested-by: Szymon Kłos <szymon.klos@collabora.com>

Change-Id: Ie63c8d7e001c90f40cf7504fd8248a6742e9d244
Reviewed-on: https://gerrit.libreoffice.org/72413Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>