Fix ShowInitialLine right side bug.

Author: BDisp

Terminal.Gui/Views/TabView/TabRow.cs

@@ -948,6 +948,21 @@ private void RenderTabLineCanvas ()
 
                             break;
                         case TabSide.Right:
+                            // Lower right tee
+                            lc.AddLine (
+                                        new (vts.X - 1, vts.Bottom),
+                                        0,
+                                        Orientation.Vertical,
+                                        tab.BorderStyle
+                                       );
+
+                            lc.AddLine (
+                                        new (vts.X - 1, vts.Bottom),
+                                        1,
+                                        Orientation.Horizontal,
+                                        tab.BorderStyle
+                                       );
+
                             break;
                         default:
                             throw new ArgumentOutOfRangeException ();

UnitTests/Views/TabViewTests.cs

@@ -3177,7 +3177,7 @@ public void Add_Three_TabsSide_Right_ShowInitialLine_False_ChangesTab_Height9 ()
 │hi             Tab1
 │              ╭────
 │              │Tab2
-│              ╭────
+│              ├────
 │              │Tab3
 │              ├────
 │              │