debug/macho: fail on invalid dynamic symbol table command

Fail out when loading a file that contains a dynamic symbol table
command that indicates a larger number of symbols than exist in the
loaded symbol table.

Thanks to Burak Çarıkçı - Yunus Yıldırım (CT-Zer0 Crypttech) for
reporting this issue.

Fixes #48990
Fixes CVE-2021-41771

Change-Id: Ic3d6e6529241afcc959544b326b21b663262bad5
Reviewed-on: https://go-review.googlesource.com/c/go/+/355990


Reviewed-by: Julie Qiu <julie@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Katie Hockman <katie@golang.org>