Drag-n-drop from zip file opened in Windows Explorer is empty

When calling `QMimeData::data("application/x-qt-windows-mime;value=\"FileContents\";index=0");` to retrieve file contents from a `QDropEvent`, an invalid buffer is returned if the source file is inside a zip file opened in windows explorer.

Steps to reproduce:

1. Compile and run the attached example
2. Open test.zip from the attached example in Windows Explorer

1. Drag test.txt into the example application

1. `QMimeData::data()` returns an invalid buffer (`QByteArray::isNull` returns `true`) and the application displays "<null>"

1. Unzip test.zip

1. Drag the new uncompressed test.txt into the example application

1. `QMimeData::data()` returns the content of test.txt and the application correctly displays the file contents: "Test!"