If an SVG file contains an empty <style> element ("<style/>"), several
assertions are triggered:

** (rsvg-convert:13649): CRITICAL **: cr_parser_new_from_buf: assertion `a_buf && a_len' failed
** (rsvg-convert:13649): CRITICAL **: cr_parser_set_sac_handler: assertion `a_this' failed
(rsvg-convert:13649): librsvg-WARNING **: Error setting CSS SAC handler
** (rsvg-convert:13649): CRITICAL **: cr_parser_destroy: assertion `a_this && PRIVATE (a_this)' failed

Testcase:

Run rsvg-convert on the following file:

<?xml version="1.0"?>
<svg>
  <defs>
    <style/>
  </defs>
</svg>

rsvg-convert version: 2.34.2 (Debian package librsvg2-bin, 2.34.2-3)