SQLChannel stops logging on LoggingSubsystem shutdown

[aleks-f]

Describe the bug

• [x] last log messages not logged on shutdown
• [x] code after main while loop in run is never reached (thread abruptly terminated?)
• [x] feature: add store-and-forward mode
• [ ] create a Util::ServerApplication-based DBLogger sample in Poco::Data which:
  • connects to a database
  • logging thread produces some logs via SQLChannel in store-and-forward mode
  • forwarding thread:
    • monitors the directory where files with *.sql extension (containing SQL inserts statements) are saved by SQLChannel in store-and-forward mode
    • executes the queries in the *.sql files
      • in case of success, deletes the *.sql file
      • in case of error, renames the offending file from *.sql to *.err
    • any files with extension different from *.sql are ignored
  • use sqlite db for the sample (like other Poco::Data samples)

[matejk]

I get this static analysis warning in SQLChannel dtor:

/poco/Data/src/SQLChannel.cpp:112:3: Call to virtual method 'SQLChannel::close' during destruction bypasses virtual dispatch [clang-analyzer-optin.cplusplus.VirtualCall]