content-sqlite: unregister on error

Problem: if content-sqlite encounters a fatal error, it may not
unregister itself from the content cache in the broker before
exiting the module thread.

Fix the control flow so the backing store is always unregistered
on failure.

Author: garlick

src/modules/content-sqlite/content-sqlite.c

@@ -832,16 +832,16 @@ int mod_main (flux_t *h, int argc, char **argv)
     if (content_register_backing_store (h, "content-sqlite") < 0)
         goto done;
     if (content_register_service (h, "content-backing") < 0)
-        goto done;
+        goto done_unreg;
     if (content_register_service (h, "kvs-checkpoint") < 0)
-        goto done;
+        goto done_unreg;
     if (flux_reactor_run (flux_get_reactor (h), 0) < 0) {
         flux_log_error (h, "flux_reactor_run");
-        goto done;
+        goto done_unreg;
     }
-    if (content_unregister_backing_store (h) < 0)
-        goto done;
     rc = 0;
+done_unreg:
+    (void)content_unregister_backing_store (h);
 done:
     content_sqlite_closedb (ctx);
     content_sqlite_destroy (ctx);