macosx: fix table column indentation (close #6929)

For indentation, the outline table column needs to be set, which used to be the title column. This is not a bad choice, since it is only column populated by all items.

However, one can't remove the outline table column easily, so I chose to disable the ability to remove it, something virtually all users don't want to do anyway.

modules/gui/macosx/MainMenu.m

@@ -434,13 +434,17 @@ static VLCMainMenu *_o_sharedInstance = nil;
         o_mi_tmp = [o_mu_playlistTableColumns addItemWithTitle:o_title
                                                         action:@selector(togglePlaylistColumnTable:)
                                                  keyEquivalent:@""];
-        [o_mi_tmp setTarget:self];
+        /* don't set a valid target for the title column selector, since we want it to be disabled */
+        if (![[o_ptc_menuorder objectAtIndex:i] isEqualToString: TITLE_COLUMN])
+            [o_mi_tmp setTarget:self];
         [o_mi_tmp setTag:i];
 
         o_mi_tmp = [o_context_menu addItemWithTitle:o_title
                                              action:@selector(togglePlaylistColumnTable:)
                                       keyEquivalent:@""];
-        [o_mi_tmp setTarget:self];
+        /* don't set a valid target for the title column selector, since we want it to be disabled */
+        if (![[o_ptc_menuorder objectAtIndex:i] isEqualToString: TITLE_COLUMN])
+            [o_mi_tmp setTarget:self];
         [o_mi_tmp setTag:i];
     }
     if (!o_mu_playlistTableColumnsContextMenu)

modules/gui/macosx/playlist.m

@@ -1363,6 +1363,8 @@
     }
     else
         [o_outline_view removeTableColumn: [o_outline_view tableColumnWithIdentifier: o_column]];
+
+    [o_outline_view setOutlineTableColumn: [o_outline_view tableColumnWithIdentifier:TITLE_COLUMN]];
 }
 
 - (void)saveTableColumns