Fix data query option allow_past to correctly work in memory mode ram and save

[stelfrag]

Summary

Fixes product@12135

when using the allow_past option in data queries and the agent memory mode is ram or save it will not
correctly detect that the after timestamp requested may be out of range, attempting to map the requested
time in invalid locations in the buffer.

Test Plan

• Start an agent in memory mode RAM and immediately
  • Run a query api/v1/data?chart=system.cpu&after=-60&options=jsonwrap
    • You should only see a few points being returned
  • Run a query api/v1/data?chart=system.cpu&after=-60&options=jsonwrap|allow_past
    • You will see 60 points returned but the results will be inconsistent; you may get null values for recent timestamps which is wrong
• After applying the PR, run the above tests
  • You will notice that the agent will correctly generate NULL values for the time range that metrics were not collected

[thiagoftsm]

The tests demonstrate the expected result. LGTM!

[odynik]

Test results looks good!
/api/v1/data?chart=system.cpu&after=-600&options=jsonwrap

      [ 1645003231, 0, 0, 0.2554278, 0.2554278, 0, 29.11877, 42.78416, 0, 13.793103],
      [ 1645003230, 0, 0, 0.0579467, 0.0579467, 0, 6.605922, 9.70607, 0, 3.129121]
  ]

/api/v1/data?chart=system.cpu&after=-60&options=jsonwrap|allow_past

      [ 1645003231, 0, 0, 0.2554278, 0.2554278, 0, 29.11877, 42.78416, 0, 13.793103],
      [ 1645003230, 0, 0, 0.0579467, 0.0579467, 0, 6.605922, 9.70607, 0, 3.129121],
      [ 1645003229, null, null, null, null, null, null, null, null, null],
      [ 1645003228, null, null, null, null, null, null, null, null, null],