Always initialise return value in compute_desc_id in rendcommon.c

Fix on e6a581f126, released in 0.2.7.1-alpha.

changes/bug16115-init-var

@@ -0,0 +1,4 @@
+  o Minor fixes (threads, comments):
+    - Always initialise return value in compute_desc_id in rendcommon.c
+      Patch by "teor".
+      Fix on e6a581f126ba, released in 0.2.7.1-alpha.

src/or/rendcommon.c

@@ -1417,7 +1417,7 @@ rend_data_dup(const rend_data_t *data)
 static int
 compute_desc_id(rend_data_t *rend_data)
 {
-  int ret;
+  int ret = 0;
   unsigned replica;
   time_t now = time(NULL);