Merge pull request dotnet/corefx#9284 from stephentoub/fix_safehandle_null

Fix OpenSslCipher.OpenKey check for valid SafeHandle

Commit migrated from https://github.com/dotnet/corefx/commit/a8eb6cef2806b698bf098fa01ffaa3924f77c7de

src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/OpenSslCipher.cs

@@ -125,10 +125,7 @@ private void OpenKey(IntPtr algorithm, byte[] key)
                 IV,
                 _encrypting ? 1 : 0);
 
-            if (_ctx == null)
-            {
-                throw Interop.Crypto.CreateOpenSslCryptographicException();
-            }
+            Interop.Crypto.CheckValidOpenSslHandle(_ctx);
 
             // OpenSSL will happily do PKCS#7 padding for us, but since we support padding modes
             // that it doesn't (PaddingMode.Zeros) we'll just always pad the blocks ourselves.