Fixed ClassCastException

53300cbbb77654fedbb4e3135eb3867e
MirakelPreferences:378
Fixed ParseException

This happened when the taskwarrior config file was deleted.
It may be caused when the user deletes all mirakel-data. The account
exists still, but the cert-files are deleted.

c2c37d66f2eec26d0e0b4bfb5e54bee4
TaskWarriorSync.java:174