Handle mod not found in versions tab

[HebaruSan]

Problem

If your mod list is empty, it should auto refresh at launch as of #2241. However, an exception is thrown instead, with this stack trace:

CKAN.ModuleNotFoundKraken: Exception of type 'CKAN.ModuleNotFoundKraken' was thrown.
   at CKAN.Registry.AllAvailable(String module)
   at CKAN.MainAllModVersions.set_SelectedModule(GUIMod value)
   at CKAN.Main.ModList_SelectedIndexChanged(Object sender, EventArgs e)
   at System.Windows.Forms.DataGridView.OnSelectionChanged(EventArgs e)

You can click Continue and then Refresh to get past this, but it should be auto-refreshing instead.

Cause

MainAllModVersions.SelectedModule calls Registry.AllAvailable without handling ModuleNotFoundKraken.

Changes

Now we catch that exception, and the auto-refresh will work.

Fixes #2298.