[clangd] Avoid null result in FindRecordTypeAt()

[nridge]

Summary

Fixes https://github.com/clangd/clangd/issues/1743

[sammccall]

Thanks!
(Both assigned reviewers are currently out on vacation)

clang-tools-extra/clangd/XRefs.cpp

auto RecordFromNode = [&AST](const SelectionTree::Node *N) {
     // (generally, one will be available for non-dependent specializations of a
     // class template).
     auto Decls = explicitReferenceTargets(N->ASTNode, DeclRelation::Underlying,
                                           AST.getHeuristicResolver());
     for (const NamedDecl *D : Decls) {
 
       if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
         // If this is a variable, use the type of the variable.
-        Records.push_back(VD->getType().getTypePtr()->getAsCXXRecordDecl());
+        if (const auto *RD = VD->getType().getTypePtr()->getAsCXXRecordDecl())
+          Records.push_back(RD);
         continue;
       }
 
       if (const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
         // If this is a method, use the type of the class.
         Records.push_back(Method->getParent());
         continue;
       }

clang-tools-extra/clangd/unittests/TypeHierarchyTests.cpp

)cpp");
   for (Position Pt : Source.points()) {
     auto Records = findRecordTypeAt(AST, Pt);
     ASSERT_THAT(Records, SizeIs(1));
     EXPECT_EQ(&findDecl(AST, "Child2"),
               static_cast<const NamedDecl *>(Records.front()));
   }
 }
 
+TEST(FindRecordTypeAt, Nonexistent) {
+  Annotations Source(R"cpp(
+    int *wa^ldo;
+  )cpp");
+  TestTU TU = TestTU::withCode(Source.code());
+  auto AST = TU.build();
+
+  for (Position Pt : Source.points()) {
+    auto Records = findRecordTypeAt(AST, Pt);
+    ASSERT_THAT(Records, SizeIs(0));
+  }
+}
+
 TEST(FindRecordTypeAt, Method) {
   Annotations Source(R"cpp(
 struct Child2 {
   void met^hod ();
   void met^hod (int x);
 };
 
 int main() {

 }
 )cpp");
 
   TestTU TU = TestTU::withCode(Source.code());
   auto AST = TU.build();
 
   for (Position Pt : Source.points()) {
     // A field does not unambiguously specify a record type
-    // (possible associated reocrd types could be the field's type,
+    // (possible associated record types could be the field's type,
     // or the type of the record that the field is a member of).
     EXPECT_THAT(findRecordTypeAt(AST, Pt), SizeIs(0));
   }
 }
 
 TEST(TypeParents, SimpleInheritance) {
   Annotations Source(R"cpp(
 struct Parent {