Kmail2 crashes when starting up. Sometimes, the application starts, but crashes when I try to open a particular mail.

Kmail Version 5.3.0 (QtWebEngine)
KDE Frameworks 5.26.0
Qt 5.6.1 (built against 5.6.1)
The xcb windowing system

Reproducible: Always

Steps to Reproduce:
1. Open kmail
2. Application crashes
3.

Actual Results:  
Application crashes

Expected Results:  
Application should work

A crash dump is provided at http://pastebin.com/5pZ8p7gf

When opening the application in a konsole, I get the following error:
[vinu@vinu ~]$ kmail this does not work on a KActionCollection containing actions! KMail got signal 11 (Exiting) Dead letters dumped. nouveau: kernel rejected pushbuf: Bad file descriptor nouveau: ch13: krec 0 pushes 1 bufs 6 relocs 0 nouveau: ch13: buf 00000000 00000002 00000004 00000004 00000000 nouveau: ch13: buf 00000001 00000007 00000002 00000002 00000000 nouveau: ch13: buf 00000002 00000008 00000002 00000002 00000000 nouveau: ch13: buf 00000003 0000000a 00000002 00000002 00000000 nouveau: ch13: buf 00000004 00000006 00000004 00000000 00000004 nouveau: ch13: buf 00000005 00000017 00000002 00000000 00000002 nouveau: ch13: psh 00000000 0000039dc0 0000039e50 nouveau: 0x200203fd nouveau: 0x00010000 nouveau: 0x00010000 nouveau: 0x20090200 nouveau: 0x00000000 nouveau: 0x01a50000 nouveau: 0x00000001 nouveau: 0x00000001 nouveau: 0x000000e6 nouveau: 0x00000000 nouveau: 0x00000001 nouveau: 0x00000000 nouveau: 0x00000000 nouveau: 0x2001054e nouveau: 0x00000000 nouveau: 0x20010487 nouveau: 0x0fac6881 nouveau: 0x80000574 nouveau: 0x200308e0 nouveau: 0x00000800 nouveau: 0x00000000 nouveau: 0x00542000 nouveau: 0xa00308e3 nouveau: 0x00000180 nouveau: 0x3f000000 nouveau: 0x3f000000 nouveau: 0x800101d5 nouveau: 0x2001054f nouveau: 0x00000000 nouveau: 0x20040360 nouveau: 0x00000000 nouveau: 0x00000000 nouveau: 0x00000000 nouveau: 0x00000000 nouveau: 0x20010674 nouveau: 0x0000003c kmail: pushbuf.c:727: nouveau_pushbuf_data: Assertion `kref' failed. QSocketNotifier: Invalid socket 14 and type 'Read', disabling... QSocketNotifier: Invalid socket 24 and type 'Read', disabling... Unable to start Dr. Konqi [vinu@vinu ~]$