settings: make displaying 'empty tag' entry optional

doc/config

@@ -378,6 +378,8 @@
 #
 #media_library_display_date = "yes"
 #
+#media_library_display_empty_tag = "yes"
+#
 #media_library_disable_two_column_mode = "no"
 #
 #enable_window_title = "yes"

doc/ncmpcpp.1

@@ -288,6 +288,9 @@ If enabled, tag editor will number tracks using format xx/yy (where xx is the cu
 .B media_library_display_date  = yes/no
 If enabled, dates of albums in media library will be displayed and respected in searching, otherwise not.
 .TP
+.B media_library_display_empty_tag  = yes/no
+If enabled, left column will contain entry for 'empty' tag, otherwise not.
+.TP
 .B media_library_disable_two_column_mode  = yes/no
 If enabled, pressing the key for the media library twice won't switch it to two column mode.
 .TP

src/media_library.cpp

@@ -196,6 +196,8 @@ void MediaLibrary::Update()
 		sort(list.begin(), list.end(), CaseInsensitiveSorting());
 		for (MPD::TagList::iterator it = list.begin(); it != list.end(); ++it)
 		{
+			if (it->empty() && !Config.media_library_display_empty_tag)
+				continue;
 			utf_to_locale(*it);
 			Artists->AddOption(*it);
 		}

src/settings.cpp

@@ -410,6 +410,7 @@ void NcmpcppConfig::SetDefaults()
 	browser_sort_by_mtime = false;
 	tag_editor_extended_numeration = false;
 	media_library_display_date = true;
+	media_library_display_empty_tag = true;
 	media_library_disable_two_column_mode = false;
 	discard_colors_if_item_is_selected = true;
 	store_lyrics_in_song_dir = false;
@@ -1047,6 +1048,10 @@ void NcmpcppConfig::Read()
 			{
 				media_library_display_date = v == "yes";
 			}
+			else if (cl.find("media_library_display_empty_tag") != std::string::npos)
+			{
+				media_library_display_empty_tag = v == "yes";
+			}
 			else if (cl.find("media_library_disable_two_column_mode") != std::string::npos)
 			{
 				media_library_disable_two_column_mode = v == "yes";

src/settings.h

@@ -247,6 +247,7 @@ struct NcmpcppConfig
 	bool browser_sort_by_mtime;
 	bool tag_editor_extended_numeration;
 	bool media_library_display_date;
+	bool media_library_display_empty_tag;
 	bool media_library_disable_two_column_mode;
 	bool discard_colors_if_item_is_selected;
 	bool store_lyrics_in_song_dir;