sql: raise an integer overflow error during CAST

Before this patch, if integer overflow occurred during casting to
integer, it was simply ignored. As a result, wrong results might take
place. Lets check possible overflows before CAST conversion, and if it
happens, raise an appropriate error.

Part of #3735

src/box/sql/vdbemem.c

@@ -532,7 +532,9 @@ sqlVdbeMemIntegerify(Mem * pMem, bool is_forced)
 		MemSetTypeFlag(pMem, MEM_Int);
 		return 0;
 	} else if ((pMem->flags & MEM_Real) != 0 && is_forced) {
-		pMem->u.i = (int) pMem->u.r;
+		if (pMem->u.r >= INT64_MAX || pMem->u.r < INT64_MIN)
+			return -1;
+		pMem->u.i = (int64_t) pMem->u.r;
 		MemSetTypeFlag(pMem, MEM_Int);
 		return 0;
 	}

test/sql/integer-overflow.result

@@ -40,3 +40,19 @@ box.sql.execute('SELECT 9223372036854775808 - 1;')
 ---
 - error: 'oversized integer: 9223372036854775808'
 ...
+-- Test that CAST may also leads to overflow.
+--
+box.sql.execute('SELECT CAST(\'9223372036854775808\' AS INTEGER);')
+---
+- error: 'Type mismatch: can not convert 9223372036854775808 to integer'
+...
+-- Due to inexact represantation of large integers in terms of
+-- floating point numbers, numerics with value < INT64_MAX
+-- have INT64_MAX + 1 value in integer representation:
+-- float 9223372036854775800 -> int (9223372036854775808),
+-- with error due to conversion = 8.
+--
+box.sql.execute('SELECT CAST(9223372036854775807.0 AS INTEGER);')
+---
+- error: 'Type mismatch: can not convert 9.22337203685478e+18 to integer'
+...

test/sql/integer-overflow.test.lua

@@ -14,3 +14,13 @@ box.sql.execute('SELECT (9223372036854775807 + 1);')
 box.sql.execute('SELECT 9223372036854775808;')
 box.sql.execute('SELECT -9223372036854775809;')
 box.sql.execute('SELECT 9223372036854775808 - 1;')
+-- Test that CAST may also leads to overflow.
+--
+box.sql.execute('SELECT CAST(\'9223372036854775808\' AS INTEGER);')
+-- Due to inexact represantation of large integers in terms of
+-- floating point numbers, numerics with value < INT64_MAX
+-- have INT64_MAX + 1 value in integer representation:
+-- float 9223372036854775800 -> int (9223372036854775808),
+-- with error due to conversion = 8.
+--
+box.sql.execute('SELECT CAST(9223372036854775807.0 AS INTEGER);')