[clang-tidy] Fix a nullptr-access crash in unused-raii-check.

[hokein]

Summary

I saw this crash in our internal production, but unfortunately didn't get
reproduced testcase, we likely hit this crash when the AST is ill-formed
(e.g. broken code).

clang-tools-extra/clang-tidy/bugprone/UnusedRaiiCheck.cpp

if (TOE->getNumArgs() == 0) {
       return;
     }
 
   // Otherwise just suggest adding a name. To find the place to insert the name
   // find the first TypeLoc in the children of E, which always points to the
   // written type.
   auto Matches =
       match(expr(hasDescendant(typeLoc().bind("t"))), *E, *Result.Context);
-  const auto *TL = selectFirst<TypeLoc>("t", Matches);
-  assert(TL);
+  if (const auto *TL = selectFirst<TypeLoc>("t", Matches))
     D << FixItHint::CreateInsertion(
         Lexer::getLocForEndOfToken(TL->getEndLoc(), 0, *Result.SourceManager,
                                    getLangOpts()),
         Replacement);
 }
 
 } // namespace bugprone
 } // namespace tidy
 } // namespace clang