[db] Concurrency issue

It seems that multiple calls from different threads may produce strange errors like:

[QT55] [W] JDBCConnector (execute:250) Query was mistaken: Data truncation: Out of range value for column 'map_y' at row 1
[QT55] [W] JDBC (doCall:56) Database exception: Data truncation: Out of range value for column 'map_y' at row 1
[QT55] [W] Servers (upd:91) Server [T1000] was not updated
[QT53] [W] DB (openIfClosed:59) Connection was previously returned (using db.close()). It might get disconnected unexpectedly.
[QT53] [W] Query (toString:461) Query was empty for action: RAW. Perhaps the implementation doesn't support that action yet?
[QT53] [W] JDBCConnector (execute:269) Invalid query
[QT53] [W] JDBC (doCall:56) Database exception: Query can not be empty. Expression: query.toString()
[QT50] [W] JDBCConnector (execute:266) Statement failed
[QT113] [W] JDBC (doCall:56) Database exception: No value specified for parameter 2
[QT54] [W] Services (getUser:78) User not found: admin
[QT50] [W] JDBC (doCall:56) Database exception: No value specified for parameter 2

Create test and fix.