Problem with cite command (tests 12)

When running a link checker over the (x)html results of the doxygen tests 12 and subdirs enabled we get the error:
```
Processing      file:///.../testing/test_output_012/html/d0/de3/citelist.xhtml

List of broken links and other issues:
file:///..../testing/test_output_012/html/
 Lines: 70, 74
  Code: 200 (no message)
 To do: Some of the links to this resource point to broken URI fragments
        (such as index.html#fragment).
The following fragments need to be fixed:
        CITEREF_LeLe12                  Lines: 70, 74
```

Also looking at the results of  rtf and docbook output we see incorrect links.
With the rtf links there is a subsequent problem of not returning the right "label" (see util.h).

1 files changed, 6 insertions, 0 deletions

diff --git a/src/util.cpp b/src/util.cpp
index 37c5e62..b51fe44 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -5179,6 +5179,12 @@ QCString rtfFormatBmkStr(const QCString &name)
   // substitute a short arbitrary string for the name
   // supplied, and keep track of the correspondence
   // between names and strings.
+  auto it = g_tagMap.find(name.str());
+  if (it!=g_tagMap.end()) // already known
+  {
+    return QCString(it->second);
+  }
+
   QCString tag = g_nextTag;
   auto result = g_tagMap.insert( std::make_pair(name.str(), g_nextTag.str()) );