Roof direction check for skillion

[justinormont]

The !this.options.roof.direction should instead check for null/undefined:

OSMBuilding/src/buildingpart.js

Line 179 in 228874c

if (this.options.roof.shape === 'skillion' && !this.options.roof.direction) {

In JavaScript, 0 is nullish, causing this warning to be printed, if you set the direction of a skillion roof to 0 (north-facing roof).

Expected behavior:

Since 0 is an acceptable roof direction, no warning should be printed.

Impact:

Minor, since I think it only causes a warning.