sql: [#2300] Fix opmitizer to conform Tarantool fields layout.

	src/lib/sqlite/src/
	* expr.c (sqlite3SetHasNullFlag): Add column to check for null,
	as Tarantool doesn't change order of fields in index. So, first
	key field in index has no number 0.
	(sqlite3FindInIndex): Pass column number of first key in index to
	check for null.
	(sqlite3CodeSubselect): Pass 0, as first column of table is always
	first.
	(sqlite3ExprCodeIN): 1. Comment. Check that aiMap containst integers
	between 0 and nVector-1 is not relevant for Tarantool. As index keys are
	references to original table columns.
	2. Check for (aiMap[i] == i) is not relevant since order of column numbers
	are original. Comment whole loop, which allocates new register range.
	3. Fix column fetch: take into account Tarantool column order.