Fix out-of-bounds writesin BitView::_Read64<true>

[chiayy-com]

This fixes #354.

[chiayy-com]

Explanation:

The original implementation had 2 issues.
The isLastField (which should be name isIncompleteField) on Line 148 is calculated incorrectly. And - 1 is not needed. (As discussed in #355) This causes the first remainderBytes (Line 158) to potentially exceed 8 and results in an illegal write.
The other issue is that the second remainderBytes (Line 187) is calucated incorrectly. Because pField has advanced 8 bytes, remainderBytes should be 8 less than the previous remainderBytes.

The latest commit I rewrote the isLastField/remainderBytes logic, and now this approach is (I believe) easier to understand and less likely to make mistake.

[chiayy-com]

Note:
I just noticed there's no test cases for this functionality in the codespace.
I did some regression testing manually (fetching proofs / quality) and it works fine, but it still need some serious tests.

(I‘d like to add some, but I'm not sure of when 😂)

[harold-b]

Yes feel free to add a test. BB currently does not have much tests, there's a few for specific cases and commonly re-used objects. But it's mostly used as a sandbox.

You can have a look in Tests.cmake.