Attempt to restore InputRoll invariant during Select All (see #3971)

I believe this method was already non-atomic so this clear operation
shouldn't change anything

src/BizHawk.Client.EmuHawk/CustomControls/InputRoll/InputRoll.cs

@@ -587,6 +587,7 @@ namespace BizHawk.Client.EmuHawk
 
 		public void SelectAll()
 		{
+			_selectedItems.Clear();
 			var oldFullRowVal = FullRowSelect;
 			FullRowSelect = true;
 			for (int i = 0; i < RowCount; i++)