fixed bug that exception happens when selection mode is set to none

Author: jingwood

Editor/ReoGridEditor.cs

@@ -875,7 +875,7 @@ void cellTypeMenuItem_Click(object sender, EventArgs e)
 
 			var menuItem = sender as ToolStripMenuItem;
 
-			if (menuItem != null && menuItem.Tag is Type && worksheet != null)
+			if (menuItem != null && menuItem.Tag is Type && worksheet != null && !worksheet.SelectionRange.IsEmpty)
 			{
 				foreach (var cell in worksheet.Ranges[worksheet.SelectionRange].Cells)
 				{

ReoGrid/Core/Range.cs

@@ -110,7 +110,15 @@ public ReferenceRange this[string address]
 			/// <returns>Instance of referenced range to worksheet</returns>
 			public ReferenceRange this[RangePosition range]
 			{
-				get { return new ReferenceRange(this.worksheet, this.worksheet.FixRange(range)); }
+				get
+				{
+					if (range.IsEmpty)
+					{
+						throw new ArgumentException("range position is empty", nameof(range));
+					} 
+
+					return new ReferenceRange(this.worksheet, this.worksheet.FixRange(range));
+				}
 			}
 		}