Allow hiding of empty presence groups: /roster {show,hide} empty (default is show)

src/config/preferences.c

@@ -522,6 +522,7 @@ _get_group(preference_t pref)
         case PREF_ROSTER:
         case PREF_ROSTER_OFFLINE:
         case PREF_ROSTER_RESOURCE:
+        case PREF_ROSTER_EMPTY:
         case PREF_ROSTER_BY:
         case PREF_RESOURCE_TITLE:
         case PREF_RESOURCE_MESSAGE:
@@ -676,6 +677,8 @@ _get_key(preference_t pref)
             return "roster.offline";
         case PREF_ROSTER_RESOURCE:
             return "roster.resource";
+        case PREF_ROSTER_EMPTY:
+            return "roster.empty";
         case PREF_ROSTER_BY:
             return "roster.by";
         case PREF_RESOURCE_TITLE:
@@ -723,6 +726,7 @@ _get_default_boolean(preference_t pref)
         case PREF_ROSTER:
         case PREF_ROSTER_OFFLINE:
         case PREF_ROSTER_RESOURCE:
+        case PREF_ROSTER_EMPTY:
             return TRUE;
         default:
             return FALSE;

src/config/preferences.h

@@ -65,6 +65,7 @@ typedef enum {
     PREF_ROSTER_SIZE,
     PREF_ROSTER_OFFLINE,
     PREF_ROSTER_RESOURCE,
+    PREF_ROSTER_EMPTY,
     PREF_ROSTER_BY,
     PREF_MUC_PRIVILEGES,
     PREF_PRESENCE,

src/config/theme.c

@@ -452,6 +452,7 @@ _load_preferences(void)
     _set_boolean_preference("roster", PREF_ROSTER);
     _set_boolean_preference("roster.offline", PREF_ROSTER_OFFLINE);
     _set_boolean_preference("roster.resource", PREF_ROSTER_RESOURCE);
+    _set_boolean_preference("roster.empty", PREF_ROSTER_EMPTY);
     _set_string_preference("roster.by", PREF_ROSTER_BY);
     if (g_key_file_has_key(theme, "ui", "roster.size", NULL)) {
         gint roster_size = g_key_file_get_integer(theme, "ui", "roster.size", NULL);