Fix undefined index errors in Display.php for guests
Notice: Undefined index: pref in /mnt/data/Web/smf21/Sources/Display.php on line 224
Guests don't have watch preferences.

Signed-off-by: Yoshi2889 <rick.2889@gmail.com>
Merge pull request #2253 from Yoshi2889/display-fix

Fix undefined index errors in Display.php for guests