If the dialog is empty, don't try to update rows.

Change-Id: I6837cc05a817815a3995647a37f0be105fad8a92
Fixes-Issue: CLIENT-487
Reviewed-on: http://gerrit.dmdirc.com/3316
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>