Immediate crash and segfault on Kdenlive master with MLT master whenever the render widget is invoked.

Since commit http://quickgit.kde.org/?p=kdenlive.git&a=commit&h=9a9346e21eed58d6d58ee9e10ecb3e88f0c39bc3
(Fix crashes when using MLT 6.2.0) and the later 8a4ebe4 requires to build it, clicking the "render" button on the toolbar or selecting "render" from the menu instantly crashes kdenlive with a segfault.  This is with Movit enabled and using MLT 6.3.0 from git master, MLT builds from  July 5 2016 and August 8 2016 pulls exact same behavior. QT and KF5 are what is in Debian Unstable as of August 10 2016 and same with what was in Debian Unstable in late July.

I was able to trace the exact offending line in commit 9a9346e to the line below in mainwindow.cpp :
 m_renderWidget->errorMessage(m_compositeAction->currentAction()->data().toInt() == 1 ? i18n("Rendering using low quality track compositing") : QString());

Reverting that line to the previous

 m_renderWidget->errorMessage(m_compositeAction->currentItem() == 1 ? i18n("Rendering using low quality track compositing") : QString());

will permit kdenlive to build and run without crashing when the renderwidget is invoked as of today. Last commit was http://quickgit.kde.org/?p=kdenlive.git&a=commit&h=f8580603474e1765289d29d00e17ca1b3289f215 


Reproducible: Always

Steps to Reproduce:
1. Build MLT from git master, build kdenlive from git master and install on Debian Unstable
2. Start kdenlive
3. click the "render" button in the toolbar or invoke "render" from the project menu

Actual Results:  
Immediate crash and segfault

Expected Results:  
Render widget appearing, displaying the options for rendering out the finished video.