setTimeContext - chokes when not in range, and never returns < 1 sample per segment

[joshStillerman]

While working on the simpleJson server for grafana I find 2 issues with setTimeContext:

1 - data() and dim_of().data() will not return < 1 sample per segment. I have a tree with 10 second segments and I ask for 1 sample every 30 seconds and I get 1 sample every 10 seconds.

2 - if the start and end are not within the tree rather than returning empty data .data() and .dim_of().data() choke.