Function guard

guard(rect: Geometry.Rect, name?: string): void
Throws an error if rectangle is missing fields or they are not valid.

Checks:
- width and height must be defined on rect
- dimensions (w & h) must not be NaN
- dimensions (w & h) must not be negative
If rect has x,y, this value is checked as well.
Parameters
- rect: Geometry.Rect
- name: string = ...
Returns void