message: Fix Android build of computecloth demo
  The NDK compiler currently fails with:
  ```
  examples/computecloth/computecloth.cpp:71:23: error: cannot
  initialize a member subobject of type 'VkSemaphore' (aka 'unsigned
  long long') with an rvalue of type 'nullptr_t'
  VkSemaphore ready{ nullptr };
  ```
diff: @@ -68,8 +68,8 @@ public:
  vks::Buffer output;
  } storageBuffers;
  struct Semaphores {
  - VkSemaphore ready{ nullptr };
  - VkSemaphore complete{ nullptr };
  + VkSemaphore ready{ 0L };
  + VkSemaphore complete{ 0L };
  } semaphores;
  vks::Buffer uniformBuffer;
  VkQueue queue;
  