If Canvas has a gameobject which has Rect Transform width or height set to 0 and this gameobject has a child with an UI element, a message 'Look rotation viewing vector is zero' is shown, when 2D view is turned on or the child is selected with Rectangle tool.

Reproduction steps:
1. Open the attached file 'case_859385_smallerProject';
2. Select Canvas/GameObject/Button;
3. Turn on 2D View in the Scene window;
4. Observe Console messages;

Reproduced with: 5.5.0f3, 5.6.0a1, 5.6.0b1
Not reproducible: 5.3.1f1, 5.4.1f1