Avoid SIGSEGV if getIOExecutor() returns null

Summary: Avoid SIGSEGV if getIOExecutor() returns null

Reviewed By: yfeldblum

Differential Revision: D16859157

fbshipit-source-id: 00c7a45677c61d84a10486f11b4f792093ac2ff5

folly/executors/GlobalExecutor.cpp

@@ -114,7 +114,12 @@ void setIOExecutor(std::weak_ptr<IOExecutor> executor) {
 }
 
 EventBase* getEventBase() {
-  return getIOExecutor()->getEventBase();
+  auto executor = getIOExecutor();
+  if (FOLLY_LIKELY(!!executor)) {
+    return executor->getEventBase();
+  }
+
+  return nullptr;
 }
 
 } // namespace folly