hello_xr reads off the end of XrExtensionProperties array

[AndrewSumsion]

In hello_xr at openxr_program.cpp:208, the application attempts to log the extensionName of a non-existent XrExtensionProperties, resulting in logging uninitialized data from the heap. It searches through the array of XrExtensionProperties, and if it doesn't find XR_KHR_composition_layer_depth, then the iterator is left at extensionProperties.end(), which does not point to a valid instance, but the code reads from it nonetheless.

if (depthExtensionProperties != extensionProperties.end()) {
    Log::Write(Log::Level::Info, Fmt("Depth submission supported (%s)", depthExtensionProperties->extensionName));
    extensions.push_back(depthExtensionProperties->extensionName);
    m_supportsDepthLayer = true;
} else {
    Log::Write(Log::Level::Info, Fmt("Depth submission NOT supported (%s)", depthExtensionProperties->extensionName)); // <-- issue here
}