[clang-tidy] Fix assert in performance-unnecessary-copy-init.

`GetDirectCallee` can be null.

Fixes #96498.

Author: legrosbuffle

clang-tools-extra/clang-tidy/utils/DeclRefExprUtils.cpp

@@ -296,7 +296,7 @@ AST_MATCHER_P(DeclRefExpr, doesNotMutateObject, int, Indirections) {
           return false;
         }
         const auto *const Method =
-            dyn_cast<CXXMethodDecl>(OpCall->getDirectCallee());
+            dyn_cast_or_null<CXXMethodDecl>(OpCall->getDirectCallee());
 
         if (Method == nullptr) {
           // This is not a member operator. Typically, a friend operator. These

clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-copy-initialization.cpp

@@ -906,3 +906,12 @@ void negativeNonConstMemberExpr() {
   }
 }
 
+
+bool operator==(ExpensiveToCopyType, ExpensiveToCopyType);
+
+template<typename T> bool OperatorWithNoDirectCallee(T t) {
+  ExpensiveToCopyType a1;
+  ExpensiveToCopyType a2 = a1;
+  return a1 == t;
+}
+