add bgm preview to the themeplaza browser

and prevent some errors

include/draw.h

@@ -51,6 +51,7 @@ typedef enum {
     INSTALL_LOADING_REMOTE_THEMES,
     INSTALL_LOADING_REMOTE_SPLASHES,
     INSTALL_LOADING_REMOTE_PREVIEW,
+    INSTALL_LOADING_REMOTE_BGM,
 
     INSTALL_NONE,
 } InstallType;