fix #21704: imported chords do not render

Recent changes to default style chordlist handling resulted in imported
scores never loading a chord list at all, causing them to render
incorrectly (no root or bass).  This is a proposed fix for that specific
issue that also addresses other potential problems in chordlist handling
(honoring the distinction between a truly empty chordlist and one that
merely contains no chord id's but does contain sym & token definitions).

libmscore/chordlist.cpp

@@ -1769,6 +1769,32 @@ bool ChordList::write(const QString& name) const
       return true;
       }
 
+//---------------------------------------------------------
+//   loaded
+//---------------------------------------------------------
 
-}
+bool ChordList::loaded() const
+      {
+      // track whether a description file has been loaded
+      // since chords.xml really doesn't load enough to stand alone,
+      // we need a way to track when a "real" chord list has been loaded
+      // for lack of anything better, key off renderListRoot
+      return !renderListRoot.isEmpty();
+      }
 
+//---------------------------------------------------------
+//   unload
+//---------------------------------------------------------
+
+void ChordList::unload()
+      {
+      clear();
+      symbols.clear();
+      fonts.clear();
+      renderListRoot.clear();
+      renderListBase.clear();
+      chordTokenList.clear();
+      }
+
+
+}

libmscore/chordlist.h

@@ -240,6 +240,8 @@ class ChordList : public QMap<int, ChordDescription*> {
       void read(XmlReader&);
       bool read(const QString&);
       bool write(const QString&) const;
+      bool loaded() const;
+      void unload();
       ChordSymbol symbol(const QString& s) const { return symbols.value(s); }
       };
 

libmscore/style.cpp

@@ -1072,11 +1072,11 @@ void StyleData::load(XmlReader& e)
                   _customChordList = true;
             else
                   _customChordList = false;
-            _chordList.clear();
+            _chordList.unload();
             }
 
       // make sure we have a chordlist
-      if (_chordList.isEmpty() && !chordListTag) {
+      if (!_chordList.loaded() && !chordListTag) {
             if (value(ST_chordsXmlFile).toBool())
                   _chordList.read("chords.xml");
             _chordList.read(newChordDescriptionFile);

mscore/bb.cpp

@@ -380,6 +380,7 @@ Score::FileError importBB(Score* score, const QString& name)
             qDebug("cannot open file <%s>\n", qPrintable(name));
             return Score::FILE_OPEN_ERROR;
             }
+      score->style()->set(StyleVal(ST_chordsXmlFile, true));
       score->style()->chordList()->read("chords.xml");
       *(score->sigmap()) = bb.siglist();
 

mscore/file.cpp

@@ -1773,6 +1773,11 @@ Score::FileError readScore(Score* score, QString name, bool ignoreVersionError)
                   if (f.open(QIODevice::ReadOnly))
                         score->style()->load(&f);
                   }
+            else {
+                  if (score->style()->value(ST_chordsXmlFile).toBool())
+                        score->style()->chordList()->read("chords.xml");
+                  score->style()->chordList()->read(score->style()->valueSt(ST_chordDescriptionFile));
+                  }
             uint n = sizeof(imports)/sizeof(*imports);
             uint i;
             for (i = 0; i < n; ++i) {