Allow 0s for maxCacheSize and maxCacheByteSize

[sraimund]

Closes #9155

Background

It is sometimes desirable to disable the cache of TileLayer.

Change List

• 0 values are now possible for maxCacheSize and maxCacheByteSize by using nullish coalescing and non-strict comparison with null.

[ibgreen]

@sraimund This looks good to me. Just some thoughts:

• Would changing the default value for the prop be cleaner or that doesn't work?
• Is there an easy way to add a minimal test case?
• Worth mentioning something in the docs or this is just a silent bug fix?

[coveralls]

coverage: 91.79%. remained the same
when pulling fb94e0c on sraimund:master
into c20af82 on visgl:master.

[sraimund]

@ibgreen Sorry, I missed two occurrences of maxCacheByteSize, that's why I amended the commit. Concerning your questions:

• I think the default values are fine (i.e., the cache is enabled by default).
• tileset-2d.spec.ts already contains two test cases for using small values of maxCacheSize and maxCacheByteSize, thus I think it's not needed to add another one. Supporting 0s is just a bit more intuitive than using 1s, which lead to the same behaviour (i.e., non-visible tiles are removed immediately from the cache).
• I added a sentence to the docs in case maxCacheByteSize is not supplied (anolog to maxCacheSize).