Fix mergebase logging on sandcastle

Summary:
D66004931 introduced mergebase logging. However, sandcastle samples still lack the column `mergebase_globalrev`.
That's because of an oversight when setting up HackEventLogger. With Sandcastle, `hg_aware = false`. This diff also sets up HackEventLogger when `hg_aware = false`.

Differential Revision: D66498071

fbshipit-source-id: a161e4768e2fb0ee8868680be919b502c4d7f787

hphp/hack/src/server/serverLazyInit.ml

@@ -1266,7 +1266,11 @@ let post_saved_state_initialization
     end else
       Option.iter
         saved_state_revs_info.ServerEnv.mergebase_globalrev
-        ~f:ServerRevisionTracker.initialize;
+        ~f:ServerRevisionTracker.initialize
+  else
+    Option.iter
+      ~f:HackEventLogger.set_mergebase_globalrev
+      saved_state_revs_info.ServerEnv.mergebase_globalrev;
   let env =
     {
       env with