Fix drag and drop bug on non-Windows platforms

[Jobsecond]

Currently, the drag and drop only works on Windows, not on macOS.

This is because file urls are different:

Platform	Path	URL	.replace('file:///', '')
Windows	D:/audio/sample.wav	file:///D:/audio/sample.wav	D:/audio/sample.wav
macOS	/Users/apple/sample.wav	file:///Users/apple/sample.wav	Users/apple/sample.wav

So, simply removing file:/// is not portable across platforms.

A portable solution is to use urls() method of QMimeData to get a list of file urls (QUrl), iterate through the list and use toLocalFile() method to convert the URL to path string.