inkscape garbles own preferences.xml

In some conditions Inkscape truncates or garbles it's own preferences.xml.
I'm running the tiles@home Client from OpenStreetMap and sometimes (very
seldom, so hard to reproduce) inkscape crashes in a way that leaves it's
~/.inkscape/preferences.xml in a garbled state (not xml) and inkscape
crashes upon the next start (see also bug #1591934)
a workaround is to delete the offending preferences file.

Other participants have reported success preventing this by
write-protecting the preferences.xml file when it contains default values
(i.e. the autogenerated one after it was deleted).

I'd suggest inkscape does not open its config read-write when in batch
mode.

I'd also suggest inkscape to fix a broken beyond repair preferences.xml
itself, by putting the default config.