FIRST(),LAST() do not return the relevant timestamp with * or multiple fields

The last() function returns different values for:
1. Select one field -- Correct value
2. Select two field in same record -- Wrong value 1970-01-01T00:00:00Z
3. With $timefilter -- Wrong value. The current time
4. Without $timefilter -- Wrong value 1970-01-01T00:00:00Z

> SELECT last("HDB_INST_DWC_POC") FROM "tenant_memory"
name: tenant_memory
time last
---- ----
2021-03-17T03:47:21.942393088Z 2.68
> SELECT last("HDB_INST_DWC_POC"), last("TOTAL") FROM "tenant_memory"
name: tenant_memory
time last last_1
---- ---- ------
1970-01-01T00:00:00Z 2.68 2.68
> SELECT last(*) FROM "tenant_memory"
name: tenant_memory
time last_HDB_INST_DWC_POC last_SUBDOMAIN last_TOTAL last_Tenant last_dev-hdb-general-01
---- --------------------- -------------- ---------- ----------- -----------------------
1970-01-01T00:00:00Z 2.68 - 2.68 x-template-srv-spring-boot-db-update-test 0
>
> SELECT last(*) FROM "tenant_memory" WHERE time > now()-6h
name: tenant_memory
time last_HDB_INST_DWC_POC last_SUBDOMAIN last_TOTAL last_Tenant last_dev-hdb-general-01
---- --------------------- -------------- ---------- ----------- -----------------------
2021-03-17T00:35:30.081580047Z 2.68 - 2.68 x-template-srv-spring-boot-db-update-test 0
> / # date
Wed Mar 17 06:36:20 UTC 2021

Reproduce the reported FIRST() and LAST() queries against the tenant_memory measurement, both with and without the time filter, and compare the returned timestamps. Then trace the query handling for single-field, multi-field, and wildcard selections. Done means all forms return the timestamp associated with the selected last record rather than the epoch or current time.

Written by the indexing model from the issue text.