potentially fix LODmap issue

[gavinr-maps]

#1384

[patrickarlt]

@gavinr-maps Do you think it would be possible to come up with a unit test that would reflect this fix?

[gavinr-maps]

@patrickarlt since this is in createTile which is called from elsewhere in Leaflet, I'm not sure how to test this. I do not see any other unit tests for this createTile function either. Could you give me some guidance?

[gavinr-maps]

@patrickarlt here is the replication case:

1. Current Behavior:
   Open https://codepen.io/gavinr/pen/gbpjJMj?editors=1010

   • Expected: the imagery layer (black and white layer) should show on load
   • Actual: the imagery layer (black and white layer) does not show on load. It does show if you zoom out then zoom back in.

2. Changes from this PR:
   Open https://codepen.io/gavinr/pen/PwqBvBL?editors=1010

   • Expected: the imagery layer (black and white layer) should show on load
   • Actual: the imagery layer (black and white layer) should shows on load

[patrickarlt]

LGTM