sql: assertion fault on select after analyze

Binary search in whereKeyStats function that uses routine
sqlite3VdbeRecordCompareMsgpack returned invalid result,
because it made wrong assumption about the number of
coinciding index columns based on _sql_stat4.
But all collected index statistics were wrong.

The analyzeOneTable routine used to call sqlite3GetTempRange
and sqlite3ReleaseTempRange functions inside of cycle intensively
changes Parser->nMem value. Thanks this pattern routine
sqlite3ReleaseTempRange could push nMem variable onto aTempReg
queue. As Parser->nMem could be bigger next time, this
variable may be used twice:

          [74, 'Column', 4, 1, 11, '', '00', 'r[11]=']
          [75, 'Column', 4, 2, 12, '', '00', 'r[12]=']
|->       [76, 'Column', 4, 3, 13, '', '00', 'r[13]=']
          [77, 'Column', 4, 4, 14, '', '00', 'r[14]=']
!rewrite  [78, 'Column', 4, 0, 13, '', '00', 'r[13]=ID']
          [79, 'MakeRecord', 13, 1, 6, '', '00',
           'r[6]=mkrec(r[13])']

Thus all assumptions about data below should be invalid and
some artifacts could exhibit.

Example:
\set language sql
CREATE TABLE t1(id INTEGER PRIMARY KEY AUTOINCREMENT, a,
		b, c, f, d, e);
CREATE INDEX i1 ON t1(a, b, c, f, d);
\set language lua
for i = 0, 100 do
    box.sql.execute(string.format("INSERT INTO t1 VALUES(null,
		    'x', 'y', 'z', 'a', %s, %s);", i,
		    math.floor(i / 2)))
end
\set language sql
SELECT * FROM "_sql_stat4";
---
['T1', 'I1', '101 101 1 1 1', '0 0 44 44 44', '0 0 44 44 44',
 ['x', 'y', 'z', 'a', 44]]
---

Expected:
---
['T1', 'I1', '101 101 101 101 1', '0 0 0 0 44', '0 0 0 0 44',
 ['x', 'y', 'z', 'a', 44]]
---

Resolves #2847.