marker group will fail and can't recover if it is attached before a tile layer is added to the map

[davidrleonard]

If a px-map-marker-group is added to a map before a tile layer is added, the marker group will fail hard. When a tile layer is added later, the marker group will not recover and draw itself.

[davidrleonard]

Fixed in 1a60ca2 (v1.2.3).

Comments from that release:

v1.2.3
==================
## Bug fixes
* Adds a default minZoom and maxZoom for map to fix a bug where marker group
  permanently fails if it attaches before a tile layer and no minZoom
  and maxZoom are defined (https://github.com/PredixDev/px-map/issues/76).
  This bug seems to be related to a limitation in the underlying library
  we use for marker group. See this issue, which seems to have solved a related
  bug in the past: https://github.com/Leaflet/Leaflet.markercluster/issues/198.
  It's possible a regression in Leaflet.markercluster caused this bug to
  happen again — this may require future investigation.