Using Print Composer on vectors rendered in symbology-ng mode crashes qgis.

[cgsbob]

Refreshing a map in Print Composer that has a vector layer rendered in symbology-ng mode causes qgis to abort with the following message:

Warning: Qt has caught an exception thrown from an event handler. Throwing
exceptions from an event handler is not supported in Qt. You must
reimplement QApplication::notify() and catch all exceptions there.

terminate called after throwing an instance of 'pal::PalException::LayerExists*'
Aborted

I heard that currently Print Composer does not work with symbology-ng mode, so I suggest that users should be prevented from using Print Composer by showing a dialog that Print Composer is currently disabled in symbology-ng mode.

[lutra]

it happens also if you don't use the new symbology, but you use the new label engine: labels do not show in the composer and if you zoom or refresh the map, qgis crashes

Warning: QMetaObject::connectSlotsByName: No matching signal for
on_buttonBox_helpRequested()
terminate called after throwing an instance of
'pal::PalException::LayerExists*'
Aborted

[wonder]

Fixed in r12174.