[HLSL] Prevent uninitialized on 2 int arguments (#173352)
Unparsed HLSL semantics have 2 int/bool arguments with default values.
Those values are loaded using checkUInt32Argument, and thus this should
never fail.
But if something is wrong in the code above (or the def changed), this
code wouldn't catch it and we'd read uninitialized integers. This
commits checks both return values and assert if one fails. On release
builds, this would early return, causing a bad codegen, but such change
will be caught by tests.
