修复FFmpeg日志路径相关的bug

ZLToolKit @ 7cb850d7

-Subproject commit ba5a796d583cd2906e06ec15c0d942e484ea1dbf
+Subproject commit 7cb850d79ba798e6d1f0bba7c655d38d2865ed92

server/FFmpegSource.cpp

@@ -63,7 +63,7 @@ void FFmpegSource::play(const string &src_url,const string &dst_url,int timeout_
 
     char cmd[1024] = {0};
     snprintf(cmd, sizeof(cmd),ffmpeg_cmd.data(),ffmpeg_bin.data(),src_url.data(),dst_url.data());
-    _process.run(cmd,File::absolutePath("",ffmpeg_log));
+    _process.run(cmd,ffmpeg_log.empty() ? "" : File::absolutePath("",ffmpeg_log));
     InfoL << cmd;
 
     if(_media_info._host == "127.0.0.1"){