Fix Database Access
Qt-5.10 and newer versions have some internal changes that cause simultaneous preparation (in different threads) of SQL queries which work on the same database to crash inside the sqlite3 engine which is shipped with Qt.
Qt-5.9 (including Qt-5.9.8) and older version seem not to exhibit this behaviour. Versions for Windows and macOS which are bundled with Qt-5.9 are not affected.
Linux users using Qt-5.10 and newer report crashes when synchronising accounts which contain an 'inv' database file.
addresses #424 (closed) #423 (closed)
closes #424 (closed) #423 (closed)