Fix crash in drop job
When a mimedata is dragged onto the desktop libplasma goes through one of two paths, one immediate, if multiple are present we show a menu and act when one is selected.
The attached mimedata from a dropevent is only valid during the initial handling. It is not safe to capture in a lambda.
This patch catpures data ahead of time.
This also fixes a bug that this async path could never have worked, it needs to call into pluginFormats. Otherwise we're looking up the mimedata 'org.kde.mediaFrame' rather than 'image/png'.
Edited by David Edmundson