Fix memory leak in font handler

The following sequence of events results in a memory leak as a font
is loaded twice
1) Invoke login screen
2) Try to log in to session, which fails
3) Back to login screen

Fix is to make sure font is deleted before being reloaded.

xrdp/xrdp_wm.c

@@ -577,6 +577,7 @@ xrdp_wm_init(struct xrdp_wm *self)
                      self->screen->bpp);
 
     /* Load the font */
+    xrdp_font_delete(self->default_font);
     dpi = xrdp_login_wnd_get_monitor_dpi(self);
     self->default_font = xrdp_font_create(self, dpi);