Fixed two SQLiteC++ Coverity Issues in Database::execAndGet() and Database::tableExists()
Fixed two SQLiteC++ Coverity Issues in Database::execAndGet() and Database::tableExists()

- adding a (void) cast in front of query.executeStep()
- adding comments explaining how errors are handled in this thow methods

Thank you to Donald Jones and Mark Pashley of Ubiquisys for reporting this to me.

layerhq/SQLiteCpp,SRombauts/SQLiteCpp,mc-server/SQLiteCpp,sergiosvieira/SQLiteCpp,SRombauts/SQLiteCpp,layerhq/SQLiteCpp,PSPDFKit-labs/SQLiteCpp,CHUYilei/SQLiteCpp,bmildner/SQLiteCpp,CHUYilei/SQLiteCpp,sndnvaps/SQLiteCpp,layerhq/SQLiteCpp,mc-server/SQLiteCpp,SRombauts/SQLiteCpp,layerhq/SQLiteCpp,hongshibao/SQLiteCpp,hongshibao/SQLiteCpp,stelalae/SQLiteCpp,bmildner/SQLiteCpp,mc-server/SQLiteCpp,PSPDFKit-labs/SQLiteCpp,SproutOrc/SQLiteCpp,bmildner/SQLiteCpp,SproutOrc/SQLiteCpp,sndnvaps/SQLiteCpp,CHUYilei/SQLiteCpp,sndnvaps/SQLiteCpp,SproutOrc/SQLiteCpp,CHUYilei/SQLiteCpp,bmildner/SQLiteCpp,PSPDFKit-labs/SQLiteCpp,sergiosvieira/SQLiteCpp,hongshibao/SQLiteCpp,sergiosvieira/SQLiteCpp