[sqlite] setting cache_size to 0 right after opening a connection is ignored

[Ousherovitch Alex]

This issue seems to have been introduced in one of the recent releases - 
setting PRAGMA cache_size to zero is a no-op and the default (2000 pages) will 
be used if it's done right after opening a database.
The reason seems to be that sPragmaNames entry for cache_size has mPragFlag 
value of zero, it probably has to be PragFlag_NeedSchema, to avoid this issue.