sql: allows only positive integer values in the LIMIT clause

VDBE returns an error if LIMIT or OFFSET expressions are casted to
the negative integer value.
If expression in the LIMIT clause can't be converted into integer
without data loss the VDBE instead of SQLITE_MISMATCH returns
SQL_TARANTOOL_ERROR with message "Only positive integers are allowed
in the LIMIT clause". The same for OFFSET clause.

Closes #3467