blockstore_processor: set block id for bank 0

[AshwinSekar]

Problem

The genesis bank did not have it's block id set.

Summary of Changes

Set it

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.2%. Comparing base (b6abf60) to head (7d27410).

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #12353     +/-   ##
=========================================
- Coverage    83.2%    83.2%   -0.1%     
=========================================
  Files         849      849             
  Lines      322519   322523      +4     
=========================================
- Hits       268527   268526      -1     
- Misses      53992    53997      +5     

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[steviez]

I typically prefer error propagation but am fine with the expect() here given that:

• confirm_full_slot() will fail if slot 0 is not full
• We do want to confirm it is a Some(_) instead of passing a None through and hiding the issue

That is, the slot will have to have been made not full between now and confirm_full_slot() (the function call above) in order for this to fail