[mod_openssl] error if ssl.engine in wrong section (fixes #2837)

error if ssl.engine in wrong section of config.
ssl.engine is valid only in global scope or $SERVER["socket"] condition

x-ref:
  "HTTPS requests timeout when cert not set for socket"
  https://redmine.lighttpd.net/issues/2837

src/mod_openssl.c

@@ -566,7 +566,8 @@ network_init_ssl (server *srv, void *p_d)
                 }
                 /* PEM file is require */
                 log_error_write(srv, __FILE__, __LINE__, "s",
-                                "ssl.pemfile has to be set");
+                                "ssl.pemfile has to be set "
+                                "when ssl.engine = \"enable\"");
                 return -1;
             }
         }
@@ -989,6 +990,12 @@ SETDEFAULTS_FUNC(mod_openssl_set_defaults)
                 }
             }
         }
+
+        if (0 != i && s->ssl_enabled && config->comp != COMP_SERVER_SOCKET) {
+            log_error_write(srv, __FILE__, __LINE__, "s",
+                            "ssl.engine is valid only in global scope "
+                            "or $SERVER[\"socket\"] condition");
+        }
     }
 
     if (0 != network_init_ssl(srv, p)) return HANDLER_ERROR;