Ensure tags are not duplicates during bookmark load

Duplicates can be introduced in several ways. User can add duplicate
tag now, but it seems tath past and current GQRX contains some bugs
related to bookmarks/tags and the saved content is sometimes crappy.

src/qtgui/bookmarks.cpp

@@ -127,7 +127,10 @@ bool Bookmarks::load()
                 QStringList TagList = strTags.split(",");
                 for(int iTag=0; iTag<TagList.size(); ++iTag)
                 {
-                  info.tags.append(&findOrAddTag(TagList[iTag].trimmed()));
+                  TagInfo *tagInfo = &findOrAddTag(TagList[iTag]);
+                  if (info.tags.indexOf(tagInfo) == -1) {
+                    info.tags.append(tagInfo);
+                  }
                 }
 
                 m_BookmarkList.append(info);