Clarifying error message in PPReadPointingDatabase()

[astronomerritt]

Fixes #1058.

• Split up exception handling in PPReadPointingDatabase().
• One error message triggers specifically if the SQL query is problematic. This would be the most common cause of failure.
• However, Joe has reported a failure for a different, unknown reason (probably file access issues due to multiple HPC runs). The second except catches all other exceptions and will include the Python error message in the message it prints to the terminal and log.

Describe your changes.

Review Checklist for Source Code Changes

• [x] Does pip install still work?
• [x] Have you written a unit test for any new functions?
• [x] Do all the units tests run successfully?
• [x] Does Sorcha run successfully on a test set of input files/databases?
• [x] Have you used black on the files you have updated to confirm python programming style guide enforcement?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.73%. Comparing base (9778aaf) to head (70d2dae). Report is 6 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1063 +/- ## ========================================== - Coverage 81.88% 81.73% -0.15% ========================================== Files 70 67 -3 Lines 3125 3094 -31 ========================================== - Hits 2559 2529 -30 + Misses 566 565 -1 ```

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