windows/registry: do not panic when data is large
windows/registry: do not panic when data is large

Allow registry blobs to be as large as 500MB

Copy of CL 14287.

Fixes golang/go#12493

Change-Id: I37b82fcf90ff2acef83c66016375fcae15e6eefc
Reviewed-on: https://go-review.googlesource.com/14288
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

npat-efault/sys,zhaoming200808/sys,zhaoming200808/sys,darkliquid/golang-sys,golang/sys,kim-racktop/sys,zhaoming200808/sys,darkliquid/golang-sys,stevenh/golang-sys,zhaoming200808/sys,stevenh/golang-sys,npat-efault/sys,stevenh/golang-sys,multiplay/golang-sys,multiplay/golang-sys,kim-racktop/sys,npat-efault/sys,kim-racktop/sys,stevenh/golang-sys,multiplay/golang-sys,darkliquid/golang-sys,darkliquid/golang-sys,golang/sys,golang/sys,npat-efault/sys,kim-racktop/sys,multiplay/golang-sys