Handle integer conversion errors (#425)

When converting a double larger or equal to math.MaxInt64 to an integer, it previously overflowed silently. It now returns an explicit error.

This fixes along the way, the math.abs(-9223372036854775808) issue.

internal/expr/functions/testdata/math_functions.sql

@@ -17,6 +17,8 @@ NULL
 2.0
 ! math.abs('foo')
 'cannot cast "foo" as double'
+! math.abs(-9223372036854775808)
+'integer out of range'
 
 -- test: math.acos
 > math.acos(NULL)