random_device: On Win32, be more lenient wrt CSP enumeration errors

[frank.richter@…]

On a machine, the Cryptographic Service Provider enumeration failed with an "Internal error"; the issue was only happening on a single machine and the cause is still unclear, however, the suspicion is that the enumeration of some CSP caused some error. Arguably, an enumeration error on some CSP shouldn't cause an abort right away, as a subsequent enumeration may succeed again and yield the requested service provider. The attached patch implements that behaviour: if an enumeration fails, don't abort altogether, but try to continue with the next CSP. This behaviour change worked around the mystery "Internal error".

[frank.richter@…]

random_device: On Win32, be more lenient wrt CSP enumeration errors

[Steven Watanabe]

Applied in ​http://github.com/boostorg/random/commit/dc2fdeac443fb56c87a03a0887c9e7c8e1d3296d