[qtbase] Return false if QDesktopServices::openUrl() fails to open file.

Previous implementation returned always true, even on cases where launch actually failed.

To test this:

- Build qtbase and install qt5-qtplatformsupport-devel package
- Build qt-wayland and install it on the device. This is needed in order to link against static lib 
- On device, download e.g. via browser an image and any file that Sailfish OS doesn't support (exe, msi, etc...)
- Launch settings from the command line
- Go the the Transfer UI -> tap supported file e.g. image -> Gallery app opens
- Tap unsupported file -> it prints to the console: Launch failed (/usr/bin/xdg-open <file name>)