Fixed missing header file function defintion

source/libublsettings-gtk3.h

@@ -762,6 +762,9 @@ char *yon_timezone_get_utc(const char *timezone);
 /// @return A newly allocated string with converted representation of bytes
 char *yon_size_long_convert_automatic_to_string(unsigned long bytes);
 
+
+char *yon_size_get_name_from_letter(char letter);
+
 /// @brief Block widget from destruction;
 void yon_gtk_widget_block_destruction(GtkWidget *target);