Vulkan example fixes

[martty]

• maxImageCount may be 0, means unlimited, handle this
• add missing sType
• change to using 1 push constant range, this results in the same functionality, but using 2 crashes my driver
  • using 2 ranges for 1 push constant block may or may not be valid, spec unclear (filed a bug against Vulkan spec to figure out)

[ocornut]

Thanks Martty. Could you replace the tabs by spaces and remove the braces where appropriate?

[martty]

sorry, changed it!

[ocornut]

Thanks :)