mplayer: try to resume playback only if a resume file actually exists

Well, this was dumb. The resume message was printed for every file,
whether a resume config file existed or not.

mpvcore/mplayer.c

@@ -888,7 +888,7 @@ exit:
 static void load_playback_resume(m_config_t *conf, const char *file)
 {
     char *fname = get_playback_resume_config_filename(file);
-    if (fname) {
+    if (fname && mp_path_exists(fname)) {
         // Never apply the saved start position to following files
         m_config_backup_opt(conf, "start");
         mp_msg(MSGT_CPLAYER, MSGL_INFO, "Resuming playback. This behavior can "