Make ReadSubKeyNames work even if key is opened with only
ENUMERATE_SUB_KEYs access rights mask.

Fixes #23869

Change-Id: I138bd51715fdbc3bda05607c64bde1150f4fe6b2
Reviewed-on: https://go-review.googlesource.com/97435Reviewed-by: Alex Brainman <alex.brainman@gmail.com>