[clangd] AddUsing: Fix a crash on ElaboratedTypes without NestedNameSpecfiiers.

clang-tools-extra/clangd/refactor/tweaks/AddUsing.cpp

if (auto *D = Node->ASTNode.get<DeclRefExpr>()) {
     if (auto *II = D->getDecl()->getIdentifier()) {
       QualifierToRemove = D->getQualifierLoc();
       Name = II->getName();
       MustInsertAfterLoc = D->getDecl()->getBeginLoc();
     }
   } else if (auto *T = Node->ASTNode.get<TypeLoc>()) {
     if (auto E = T->getAs<ElaboratedTypeLoc>()) {
       QualifierToRemove = E.getQualifierLoc();
+      if (!QualifierToRemove)
+        return false;
 
       auto SpelledTokens =
           TB.spelledForExpanded(TB.expandedTokens(E.getSourceRange()));
       if (!SpelledTokens)
         return false;
       auto SpelledRange = syntax::Token::range(SM, SpelledTokens->front(),
                                                SpelledTokens->back());
       Name = SpelledRange.text(SM);

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

public:
   // Do not offer code action when operating on a banned namespace.
   EXPECT_UNAVAILABLE(Header + "void fun() { ban::fo^o(); }");
   EXPECT_UNAVAILABLE(Header + "void fun() { ::ban::fo^o(); }");
   EXPECT_AVAILABLE(Header + "void fun() { banana::fo^o(); }");
 
   // Do not offer code action on typo-corrections.
   EXPECT_UNAVAILABLE(Header + "/*error-ok*/c^c C;");
 
+  // NestedNameSpecifier, but no namespace.
+  EXPECT_UNAVAILABLE(Header + "class Foo {}; class F^oo foo;");
+
   // Check that we do not trigger in header files.
   FileName = "test.h";
   ExtraArgs.push_back("-xc++-header"); // .h file is treated a C by default.
   EXPECT_UNAVAILABLE(Header + "void fun() { one::two::f^f(); }");
   FileName = "test.hpp";
   EXPECT_UNAVAILABLE(Header + "void fun() { one::two::f^f(); }");
 }