fix: only set filter once for intial filters
fix: only set filter once for intial filters

Fixes #258

When filters are applied before the first node has
been set the observable created uses the requested
key observable to cache the node. It should only use
the first item for each call, otherwise each new
navigation will cause the same filter to be set again,
overwriting any other filters.

mapillary/mapillary-js,mapillary/mapillary-js