d1: fix RowsAffected() in sql.Result implementation

[b0ch3nski]

What

This change fixes RowsAffected() method on sql.Result interface implementation for D1.

Motivation

RowsAffected() function is currently broken because it looks for changes in result before fetching meta first - this results in panic:

panic: syscall/js: call of Value.Int on undefined
goroutine 1 [running]:
syscall/js.Value.float({{}, 0x0, 0x0}, {0x940c0, 0x9})
	syscall/js/js.go:523 +0x10
syscall/js.Value.Int(...)
	syscall/js/js.go:540
github.com/syumai/workers/cloudflare/d1.(*result).RowsAffected(0x9032a0)
github.com/syumai/workers@v0.30.2/cloudflare/d1/result.go:29 +0x7

Docs states how the D1Result looks like.

[syumai]

Thanks! 👍