Only add features to unrenderedFeatures when drawFeature returns false

[ahocevar]

Renderer::drawFeature returns undefined for features without a geometry, and false for features that were not rendered. Renderer.SVG::drawFeature returns null for features that were drawn incompletely (i.e. clipped because the extent exceeds the coordinate range). But Layer.Vector adds features to the unrenderedFeatures array for every falsish return from Renderer::drawFeature. Instead, it should only add features where drawFeature returns false or null. When we get rid of Renderer.SVG, we only need to check for false.

[ahocevar]

All tests pass (except Control.Measure, but they also fail without the patch). Thanks for any review.

[erilem]

Replying to ahocevar:

All tests pass (except Control.Measure, but they also fail without the patch). Thanks for any review.

We've got timing issues with the Control.Measure tests. They should eventually pass if you run them multiple times.

[erilem]

Thanks Andreas. Please commit.

[ahocevar]

(In [11853]) only add features to the unrendererdFeatures array when they were not drawn due to lack of geometry. r=erilem (closes #3235)"