Random case extension causes Inkscape to crash (0.92.x, master, Python 3 and Python 2)

Steps to reproduce:

• open Inkscape
• type a text with a couple of letters, like 'ahgahg'
• Extensions > Text > Change case > Random case

What happened?

Inkscape crashes with inkscape_debug_trace_2019.03.31.23.23.05.txt

The temporary file recovered from the /tmp folder: ink_ext_XXXXXX.svgS690ZZ

What should have happened?

No crash, random case on text.

Inkscape Version and Operating System:

• Inkscape Version: 0.92.x, Python 2 and Python 3
• Operating System: Linux Mint 19.1