[clang-tidy] Fix null pointer dereference in readability-identifier-naming
readability-identifier-naming causes a null pointer dereference when checking an identifier introduced by a structured binding whose right hand side is an undeclared identifier.
Running the check on a file that is just the following results in a crash:
auto [left] = right;
Patch by Mark Stegeman!
Reviewers: alexfh, hokein, aaron.ballman, JonasToth
Reviewed By: hokein, aaron.ballman
Subscribers: madsravn, xazax.hun, cfe-commits
Tags: #clang-tools-extra, #clang
Differential Revision: https://reviews.llvm.org/D62404