Fix: Recording a frame while unpaused, immediately after an undo, could merge unrelated undo actions.

Author: SuuperW

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.MenuItems.cs

@@ -285,6 +285,7 @@ private void EditSubMenu_DropDownOpened(object sender, EventArgs e)
 		private void UndoMenuItem_Click(object sender, EventArgs e)
 		{
 			CurrentTasMovie.ChangeLog.Undo();
+			_extendNeedsMerge = false;
 		}
 
 		private void RedoMenuItem_Click(object sender, EventArgs e)

src/BizHawk.Client.EmuHawk/tools/TAStudio/UndoHistoryForm.cs

@@ -87,7 +87,8 @@ private void UndoToHere(int index)
 			{
 				while (Log.UndoIndex > index)
 				{
-					Log.Undo();
+					// Although we have a reference to the Log, TAStudio needs to do a little extra on undo.
+					_tastudio.UndoExternal();
 				}
 			});