Crash when adding .md to --sourceext

[janedegtiareva]

I would like to be able to define source snippet in a .md file using a syntax similar to .xml source files. If I do that right now and add .md file to sourcceext, the tool crashes.

I am running the following command:
mdinject --root=../rust --docsroot=. --sourceext=".ts|.js|.xml|.md" --targetext=".md|.txt" -w

The issue occurs even if the README.md file in the source dir is empty or is a simple .md file with no snippet annotations.