Fix red X on HideTab

[HebaruSan]

Problem

If you install a mod with recommendations, suggestions, or a provides dependency in GUI on Linux with a recent-ish version of Mono, you get a big red X when you accept the recommendations or provides selection prompt:

This was observed on Mono 5.14.0.177, but it works fine on Mono 5.10.1.20. Intermediate versions have not yet been tested.

Cause

As of some recent version of Mono, it's apparently no longer safe to hide the active tab of a TabControl. The control keeps the active tab index as it was, pointing to the removed tab, and then when the runtime attempts to draw the control, it tries to use that index to get the active tab, which doesn't work because it's gone:

System.ArgumentOutOfRangeException: ControlCollection does not have that many controls
Parameter name: index
Actual value was 3.
  at System.Windows.Forms.Control+ControlCollection.get_Item (System.Int32 index) [0x00027] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.TabControl.GetTab (System.Int32 index) [0x00006] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.TabControl.GetTabRect (System.Int32 index) [0x00000] in <185f5064526646d192550947861d97b1>:0 
  at (wrapper remoting-invoke-with-check) System.Windows.Forms.TabControl.GetTabRect(int)
  at System.Windows.Forms.Theming.Default.TabControlPainter.Draw (System.Drawing.Graphics dc, System.Drawing.Rectangle area, System.Windows.Forms.TabControl tab) [0x000df] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.ThemeWin32Classic.DrawTabControl (System.Drawing.Graphics dc, System.Drawing.Rectangle area, System.Windows.Forms.TabControl tab) [0x0000a] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.TabControl.Draw (System.Drawing.Graphics dc, System.Drawing.Rectangle clip) [0x00005] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.TabControl.OnPaintInternal (System.Windows.Forms.PaintEventArgs pe) [0x00017] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.Control.WmPaint (System.Windows.Forms.Message& m) [0x0006d] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.Control.WndProc (System.Windows.Forms.Message& m) [0x001a4] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.TabControl.WndProc (System.Windows.Forms.Message& m) [0x00057] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.Control+ControlWindowTarget.OnMessage (System.Windows.Forms.Message& m) [0x00000] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.Control+ControlNativeWindow.WndProc (System.Windows.Forms.Message& m) [0x0000b] in <185f5064526646d192550947861d97b1>:0 
  at System.Windows.Forms.NativeWindow.WndProc (System.IntPtr hWnd, System.Windows.Forms.Msg msg, System.IntPtr wParam, System.IntPtr lParam) [0x00085] in <185f5064526646d192550947861d97b1>:0 

(However, the actual code for TabControl hasn't changed in many years. Maybe it's a new race condition due to threading changes in the draw logic? Who knows.)

This happens in two places currently:

CKAN/GUI/MainInstall.cs

Line 133 in 37c8477

tabController.HideTab("ChooseRecommendedModsTabPage");

CKAN/GUI/MainDialogs.cs

Line 69 in 37c8477

tabController.HideTab("ChooseProvidedModsTabPage");

It can also be made to happen in a third place if we move a HideTab call before a ShowTab call:

CKAN/GUI/MainChangeset.cs

Lines 108 to 109 in 37c8477

	tabController.ShowTab("ManageModsTabPage");
	tabController.HideTab("ChangesetTabPage");

Changes

Luckily we already have a TabController wrapper, so we can work around this cleanly.

Now TabController.HideTab calls DeselectTab if the tab it's hiding is selected (which Mono should be doing itself anyway). This makes it safe to hide tabs again.

Fixes #2499.

[Stigmate-Fr]

It work greats after compiling on ubuntu 18.04 ! THANK YOU !

[smythe811]

Confirmed, recompiled on Mint 19 (18.04 base) and this corrected the issue in #2499.

[politas]

A nice clean fix, looks good to me!. I'll merge and push out a new release tonight/tomorrow.