Fix test. Close #216
Fix test. Close #216

When one goroutine close db that opended as :memory:, session
will be lost. So another goroutine can't refer the last session.
goroutine .

helight/helight_code,accense/go-sqlite3,joewalnes/go-sqlite3,accense/go-sqlite3,andviro/go-sqlite3,mattn/go-sqlite3,helight/helight_code,xeodou/go-sqlcipher,accense/go-sqlite3,danderson/go-sqlite3,lyonel/go-sqlite3,danderson/go-sqlite3,helight/helight_code,helight/helight_code,shaxbee/go-sqlite3,ArtemTeleshev/go-sqlite3,andviro/go-sqlite3,helight/helight_code,shaxbee/go-sqlite3,helight/helight_code,lyonel/go-sqlite3,helight/helight_code,mattn/go-sqlite3,ArtemTeleshev/go-sqlite3,hujunlong/go-sqlite3,ArtemTeleshev/go-sqlite3,danderson/go-sqlite3,mattn/go-sqlite3,helight/helight_code,lyonel/go-sqlite3,joewalnes/go-sqlite3,helight/helight_code,hujunlong/go-sqlite3,xeodou/go-sqlcipher,xeodou/go-sqlcipher,shaxbee/go-sqlite3,hujunlong/go-sqlite3,joewalnes/go-sqlite3,andviro/go-sqlite3