Fix sequence and integrate in MySQL storage implementation

[roger2hk]

#21

This PR fixes the panic error when adding new entry to a zero-size log. There is a TODO to modify the query (probably use left outer join)/logic if the given tileIDs are not sorted and may not exist.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 31.05%. Comparing base (46ec9c2) to head (b9cc9e3).
Report is 21 commits behind head on main.

Files	Patch %	Lines
storage/mysql/mysql.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
- Coverage   35.80%   31.05%   -4.75%     
==========================================
  Files          16       16              
  Lines        1363     1565     +202     
==========================================
- Hits          488      486       -2     
- Misses        801     1005     +204     
  Partials       74       74              

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