Backport: SL-15383 Controls table was empty after canceling advanced graphical settings

Also causes crashes on SearchableControl::setHighlighted due to views not being there

indra/newview/llfloaterpreference.cpp

@@ -3458,10 +3458,15 @@ void LLPanelPreferenceControls::cancel()
         if (mConflictHandler[i].hasUnsavedChanges())
         {
             mConflictHandler[i].clear();
+			if (mEditingMode == i)
+			{
+				// cancel() can be called either when preferences floater closes
+				// or when child floater closes (like advanced graphical settings)
+				// in which case we need to clear and repopulate table
+				regenerateControls();
+			}
 		}
     }
-    pControlsTable->clearRows();
-    pControlsTable->clearColumns();
 }
 
 void LLPanelPreferenceControls::saveSettings()