Bug 1597150 - Bump RLBox library to the latest version. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D53374

--HG--
extra : moz-landing-system : lando

third_party/rlbox/README-mozilla

@@ -1,7 +1,7 @@
 This directory contains the rlbox source from the upstream repo:
 https://github.com/PLSysSec/rlbox_sandboxing_api/
 
-Current version: [commit 521dcd664b60d03e7b7082199407fa20c3f812b7]
+Current version: [commit 5f107fed30f2dc578ca4f82dc3c7d3907abbd86b]
 
 UPDATING:
 

third_party/rlbox/include/rlbox_policy_types.hpp

@@ -123,6 +123,14 @@ class sandbox_callback
   }
 
 public:
+  sandbox_callback()
+    : sandbox(nullptr)
+    , callback(nullptr)
+    , callback_interceptor(nullptr)
+    , callback_trampoline(0)
+    , key(nullptr)
+  {}
+
   sandbox_callback(sandbox_callback&& other)
   {
     move_obj(std::forward<sandbox_callback>(other));