agent: Fix compiler warning when building with clang

Fixes: 8b467ad39a76 ("agent: Add option to open socket as specific user")

src/libstrongswan/plugins/agent/agent_private_key.c

diff --git a/src/libstrongswan/plugins/agent/agent_private_key.c b/src/libstrongswan/plugins/agent/agent_private_key.c
index c1d371c..802298c 100644
--- a/src/libstrongswan/plugins/agent/agent_private_key.c
+++ b/src/libstrongswan/plugins/agent/agent_private_key.c
@@ -188,6 +188,7 @@
 				close(s);
 				return -1;
 			case 0:
+			{
 				/* child, do everything manually to avoid interacting with
 				 * mutexes etc. that are potentially locked in the parent */
 				struct passwd *pwp;
@@ -209,6 +210,7 @@
 				}
 				exit(EXIT_FAILURE);
 				/* not reached */
+			}
 			default:
 				/* parent */
 				if (waitpid(pid, &status, 0) == -1 ||