[asan] Restore check removed by r332033

[waltl]

Summary

Needed by fiber handling code, and possibly other code paths.

lib/asan/asan_thread.h

return !atomic_load(&stack_switching_, memory_order_relaxed) &&
            (reinterpret_cast<uptr>(fake_stack_) > 1);
   }
 
   FakeStack *fake_stack() {
     if (!__asan_option_detect_stack_use_after_return)
       return nullptr;
     if (atomic_load(&stack_switching_, memory_order_relaxed))
       return nullptr;
+    if (!has_fake_stack())
+      return AsyncSignalSafeLazyInitFakeStack();
     return fake_stack_;
   }
 
   // True is this thread is currently unwinding stack (i.e. collecting a stack
   // trace). Used to prevent deadlocks on platforms where libc unwinder calls
   // malloc internally. See PR17116 for more details.
   bool isUnwinding() const { return unwinding_; }
   void setUnwinding(bool b) { unwinding_ = b; }