Backport gtlscertificate: Fix bug in PEM private key parser to glib-2-58
Make sure to not go outside of PEM data buffer when looking for private key.
Also adding test case that triggers this bug.
Backport of !534 (merged).
Make sure to not go outside of PEM data buffer when looking for private key.
Also adding test case that triggers this bug.
Backport of !534 (merged).