fixes [v4.6.3.1520]

-A memory leak fix in  TAsTableInfo.Add(-,-): pks list wasn't being
freed
-Handle ShowEditForm (which creates a AsDbForm for the selected table)
in MainForm in case something goes wrong
-Implementations of IAsDbmetada tweaked for all dbtypes.
-Fix for SQLDB's TMSSQLConnection "Error 20019 : Attempt to initiate a
new Adaptive Server operation with results pending" (happened
sometimes) by setting TAsQuery.FQuery.PacketRecord to -1 (on creation)