Fix broken reuse of deleted entries in key map file

[jeltz]

Since we tried to check if flags & MAP_ENTRY_EMPTY was true when searching for empty entries the code was broken since x & 0 always is false. We fix this by refactoring pg_tde_read_one_map_entry() so the filtering of the entries is done outside the function. This make implementing search for empty entries much easier.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.71429% with 3 lines in your changes missing coverage. Please review.

Project coverage is 76.06%. Comparing base (a6f774e) to head (2cf9f20).

❌ Your project status has failed because the head coverage (76.06%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@                  Coverage Diff                  @@
##           TDE_REL_17_STABLE     #239      +/-   ##
=====================================================
- Coverage              76.17%   76.06%   -0.11%     
=====================================================
  Files                     22       22              
  Lines                   2455     2448       -7     
  Branches                 383      384       +1     
=====================================================
- Hits                    1870     1862       -8     
- Misses                   511      513       +2     
+ Partials                  74       73       -1     

Components	Coverage Δ
access	72.41% <85.71%> (-0.50%)	⬇️
catalog	86.24% <ø> (ø)
common	92.50% <ø> (ø)
encryption	71.90% <ø> (ø)
keyring	69.87% <ø> (ø)
src	52.80% <ø> (ø)
smgr	96.93% <ø> (ø)
transam	∅ <ø> (∅)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.