TypeError when OpenSSL library is not found on Windows #316
Description
On Windows, importing bitcoin.core.key can crash with a TypeError
when the OpenSSL library is not found.
This appears to happen because ctypes.util.find_library() may return
None on Windows, which is then passed directly to
ctypes.cdll.LoadLibrary().
Steps to reproduce
On a Windows system without OpenSSL available on PATH:
python -c "import bitcoin.core.key"
I have a small patch that adds an explicit check and raises a clearer error
on Windows instead of crashing.
Would be happy to open a PR if this approach sounds reasonable.