tiled 1.7.0 crashes when pasting multiple layers

[HoraK-FDF]

here is what i did do produce the crash made it several times:

• opened the map https://github.com/themanaworld/tmwa-client-data/blob/master/maps/099-7.tmx
• selected all tile and object layers
• selected all in menu-bar and did copy in menu-bar
• opened the map https://gitlab.com/themanaworld/evolved/clientdata/-/blob/0d5262ba6d59ddd73c93415f2b48b5404558cbfa/maps/099-7.tmx
• removed all layers expect the Fringe layer
• choose paste in menu-bar
• moved mouse over to map window ---> crash

[bjorn]

Hrm, strange, I could reproduce this reliably twice with the released AppImage, but with a local build of the v1.7.0 tag I have not been able to crash it yet. The AppImage reveals the following code involved in the crash:

Thread 1 "tiled" received signal SIGSEGV, Segmentation fault.
0x00007ffff6819630 in Tiled::Layer::isHidden() const ()
   from /home/bjorn/Downloads/linux-64bit/squashfs-root/usr/bin/../lib/libtiled.so
(gdb) bt
#0  0x00007ffff6819630 in Tiled::Layer::isHidden() const () from /home/bjorn/Downloads/linux-64bit/squashfs-root/usr/bin/../lib/libtiled.so
#1  0x00005555554bd141 in Tiled::AbstractTileTool::updateBrushVisibility() ()
#2  0x00005555555b71a0 in Tiled::MapScene::event(QEvent*) ()

This suggests there has been a faulty Layer pointer returned from AbstractTileTool::targetLayersForStamp.

[bjorn]

Pushed a fix. That was a silly mistake I made in c87f8c4. :-(