Fix bug when circle is the only layer on the map

[Falke-Design]

When circle was the only layer on the map, the hidden snapping-border circle was making problems while edit mode.

Fix: #640
Fix: #652

[codeofsumit]

This seems to be quite custom.
Couldn’t we utilize pmTempLayer For this?

https://github.com/Falke-Design/leaflet.pm/blob/circle_bug/src/js/Mixins/Snapping.js#L264

Maybe I misunderstand the problem here - can you explain it more?

[Falke-Design]

No because of the line from you, the snapping will not work on _pmTempLayer layers. So I can't use this flag for the hidden Circle, where I want to snap.

So when I have one Circle on the map and I edit them, then a hidden Circle for snapping to the borders is created. Because of this new hidden layer, the available snapping layers is greater then 1. Then a snapList will be created.
But in the function _calcClosestLayer the snapping to the own circle border from the "parent" circle is not allowed Snapping.js#L282. Now no other layer is on the map where can be snapped, so Snapping.js#L277 will returned empty and then it runs in _checkPrioritiySnapping() into a empty object and crashs Snapping.js#L171.

When more then one Circle is drawn on the map, there will never returned an empty Object.