messenger callbacks having return values ignored in validation layer

[rpavlik]

Found with clang-tidy:

OpenXR-SDK-Source/src/api_layers/core_validation.cpp:270:34: warning: Value stored to 'ret_val' during its initialization is never read [clang-analyzer-deadcode.DeadStores]
                        XrBool32 ret_val = messenger_create_info->userCallback(debug_utils_severity,

It's not being used because this call (and many including it) are void return. I think it should at least abort the loop, though.

Fairly low priority.

cc @daveh-lunarg

[rpavlik-bot]

An issue (number 1288) has been filed to correspond to this issue in the internal Khronos GitLab.

If you have a Khronos account, you can access that issue at KHR:openxr/openxr#1288.