GH715: ENGINE_finish can take NULL

Simplifies calling code.  Also fixed up any !ptr tests that were
nearby, turning them into NULL tests.

Reviewed-by: Richard Levitte <levitte@openssl.org>

ssl/ssl_ciph.c

@@ -439,8 +439,7 @@ static int get_optional_pkey_id(const char *pkey_name)
                                     ameth) <= 0)
             pkey_id = 0;
     }
-    if (tmpeng)
-        ENGINE_finish(tmpeng);
+    ENGINE_finish(tmpeng);
     return pkey_id;
 }