Deal with threading and download errors

[HebaruSan]

Problems

As of #2351, I'm getting these errors when trying to install a mod on Windows:

System.ArgumentException: Controls created on one thread cannot be parented to a control on a different thread.
   at System.Windows.Forms.Control.ControlCollection.Add(Control value)
   at System.Windows.Forms.ToolStripControlHost.SyncControlParent()
   at System.Windows.Forms.ToolStripControlHost.OnParentChanged(ToolStrip oldParent, ToolStrip newParent)
   at System.Windows.Forms.ToolStripItem.set_ParentInternal(ToolStrip value)
   at System.Windows.Forms.ToolStrip.SetDisplayedItems()
   at System.Windows.Forms.StatusStrip.SetDisplayedItems()
   at System.Windows.Forms.ToolStrip.OnLayout(LayoutEventArgs e)
   at System.Windows.Forms.StatusStrip.OnLayout(LayoutEventArgs levent)
   at System.Windows.Forms.Control.PerformLayout(LayoutEventArgs args)
   at System.Windows.Forms.ToolStrip.DoLayoutIfHandleCreated(ToolStripItemEventArgs e)
   at System.Windows.Forms.ToolStrip.OnItemVisibleChanged(ToolStripItemEventArgs e, Boolean performLayout)
   at System.Windows.Forms.ToolStripItem.OnVisibleChanged(EventArgs e)
   at System.Windows.Forms.ToolStripItem.SetVisibleCore(Boolean visible)
   at System.Windows.Forms.ToolStripControlHost.SetVisibleCore(Boolean visible)
   at CKAN.Main.ShowWaitDialog(MainCancelCallback cancelAction)
   at CKAN.Main.InstallMods(Object sender, DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)

Of course this works fine on Linux. Three cheers for "write once run anywhere."

If a downloaded file doesn't pass validation (invalid ZIP, wrong file size or hashes), a few problems happen:

• The error message doesn't name the mod with the problem, which makes it harder for the user to deal with it
• The error message is displayed by the uncaught exceptions handler, so the GUI ends up in an inconsistent state or crashes outright
• Other mods in the same download batch may be discarded instead of being added to the cache, even if they are valid

Causes

WinForms on Windows only allows its GUI controls to be accessed from certain threads; other threads have to call Control.Invoke to pass code to be run on the appropriate thread. I assume this has to do with it being a wrapper around code from the 1990s, because if you were designing a GUI framework from scratch, you'd probably design it to not care about this sort of thing.

That's why Util.Invoke is sprinkled throughout the GUI code. The above exception happened on this line:

CKAN/GUI/MainWait.cs

Line 27 in a6619fe

StatusProgress.Visible = true;

... which was being called from a background thread without Invoke.

Changes

Now Util.Invoke calls are added to all affected functions in MainWait.cs. The status bar progress bar is in a separate block because I found instances during investigation where putting it in the same Invoke as the regular progress bar wasn't good enough.

InvalidModuleFileKraken is now caught and displayed to the user in NetAsyncModulesDownloader.ModuleDownloadsComplete, which allows the loop to finish caching all the downloaded mods.

The mod name and version are added to the text for InvalidModuleFileKraken.