In Wayland the clipboard changes anytime the focused window changes, which happens when opening the PasteDialog.
In order to support this case, just check that chosen mimetype is still available after the dialog returns.
CCBUG: 421974
This fixes the case:
- launch spectacle, take any screenshot
- click on copy to clipboard
- in dolphin, right click > paste clipboard content
- a popup opens, type in a file name (any), click on ok
Needs qt/qt/qtwayland!18 (merged) qt/qt/qtwayland!21 (merged)