CTextBox: Fix unselectable textbox of one line

CTextBox.cs

@@ -9,17 +9,16 @@ namespace CsvView
     {
         public CTextBox()
         {
-            Multiline = true;
             WordWrap = false;
             ScrollBars = ScrollBars.Horizontal;
             Font = new Font("Courier New", 9, FontStyle.Regular, GraphicsUnit.Point, 0);
         }
-
+        
         [DllImport("user32.dll")]
         private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);
 
         private const int WM_MOUSEWHEEL = 0x20a;
-
+        
         protected override void WndProc(ref Message m)
         {
             if (m.Msg == WM_MOUSEWHEEL)

FrmCsvViewer.cs

@@ -185,6 +185,7 @@ namespace CsvView
                 Anchor = (AnchorStyles.Top | AnchorStyles.Left | AnchorStyles.Right),
                 Width = pnlData.Width - Padding,
                 Height = (valueLines.Length * LineHeight) + TexboxPadding,
+                Multiline = (valueLines.Length > 1),
                 Top = y,
                 Left = 0,
                 ReadOnly = true,