DXC crashes on bad shader register input

[damyanp]

Description

StructuredBuffer<uint> foo : FOO(123);
void main() {} // unneeded

This crashes on latest dxc.

[tcorringham]

A non-null parenthesized list following a semantic is mis-parsed as a direct initializer. When the semantic actions for a direct initializer are performed the type of the initializer is dereferenced - however as a semantic doesn't have a type this results in dereferencing NULLPTR which causes the crash.
As semantics don't accept parameters any parenthesized list following a semantic is an error, and an error diagnostic should be generated.

[tcorringham]

This has now been fixed by #7729, so I am closing this issue.