sql: [2302] Enable re-seeking of Tarantool cursors when in stale state.

	src/box/
	* sql.c (tarantoolSqlite3MovetoUnpacked): Add imaginary opcode (255) to
	signal Tarantool to re-seek the cursor.

	src/lib/sqlite/src/
	* btree.c (btreeMoveto): Pass imagbiary opcode (instead of garbage).
	(sqlite3BtreeNext): If Tarantool's cursor in invalid state - restore it.