config-parser: add missing return for an error case

Fixes
config-parser.c: In function 'handle_key':
config-parser.c:81: error: control reaches end of non-void function

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/shared/config-parser.c b/shared/config-parser.c
index 10f6f12..5ffa466 100644
--- a/shared/config-parser.c
+++ b/shared/config-parser.c
@@ -78,6 +78,8 @@
 		assert(0);
 		break;
 	}
+
+	return -1;
 }
 
 int