[clang-format] Fix namespace end comments fixer with anonymous namespaces.

[curdeius]

Summary

Previously, a strange trailing comment was produced:

namespace out { namespace {
}} // namespace out::

(mind the "out::").

[MyDeveloperDay]

LGTM

clang/lib/Format/NamespaceEndCommentsFixer.cpp

if (Style.CompactNamespaces) {
           StartLineIndex - CompactedNamespacesCount - 1 ==
               AnnotatedLines[I + 1]->MatchingOpeningBlockLineIndex &&
           !AnnotatedLines[I + 1]->First->Finalized) {
         if (hasEndComment(EndCommentPrevTok)) {
           // remove end comment, it will be merged in next one
           updateEndComment(EndCommentPrevTok, std::string(), SourceMgr, &Fixes);
         }
         ++CompactedNamespacesCount;
+        if (!NamespaceName.empty())
           AllNamespaceNames = "::" + NamespaceName + AllNamespaceNames;
         continue;
       }
       NamespaceName += AllNamespaceNames;
       CompactedNamespacesCount = 0;
       AllNamespaceNames = std::string();
     }
     // The next token in the token stream after the place where the end comment
     // token must be. This is either the next token on the current line or the

clang/unittests/Format/NamespaceEndCommentsFixerTest.cpp

EXPECT_EQ("namespace out { namespace in {\n"
             "int i;\n"
             "int j;\n"
             "};}// namespace out::in",
             fixNamespaceEndComments("namespace out { namespace in {\n"
                                     "int i;\n"
                                     "int j;\n"
                                     "};}",
                                     CompactNamespacesStyle));
+  EXPECT_EQ("namespace out { namespace {\n"
+            "int i;\n"
+            "int j;\n"
+            "}}// namespace out",
+            fixNamespaceEndComments("namespace out { namespace {\n"
+                                    "int i;\n"
+                                    "int j;\n"
+                                    "}}",
+                                    CompactNamespacesStyle));
 
   // Adds an end comment after a semicolon.
   EXPECT_EQ("namespace {\n"
             "int i;\n"
             "int j;\n"
             "};// namespace",
             fixNamespaceEndComments("namespace {\n"
                                     "int i;\n"
EXPECT_EQ("namespace out { namespace in {\n"
                                     CompactNamespacesStyle));
   EXPECT_EQ("namespace out { namespace in {\n"
             "}\n"
             "} // namespace out::in",
             fixNamespaceEndComments("namespace out { namespace in {\n"
                                     "}// banamespace in\n"
                                     "} // namespace out",
                                     CompactNamespacesStyle));
+  EXPECT_EQ("namespace out { namespace {\n"
+            "}} // namespace out",
+            fixNamespaceEndComments("namespace out { namespace {\n"
+                                    "}} // namespace out::",
+                                    CompactNamespacesStyle));
 }
 
 TEST_F(NamespaceEndCommentsFixerTest, UpdatesInvalidMacroEndLineComment) {
   FormatStyle Style = getLLVMStyle();
   Style.NamespaceMacros.push_back("TESTSUITE");
 
   EXPECT_EQ("TESTSUITE() {\n"
             "int i;\n"