This situation happens when a file with a text effect sequencer strip is
loaded in Blender < 2.76 and saved. This destroys the effect data, causing
a crash in Blender ≥ 2.76.
d2f748a222 prevented the crash when opening such a file, but accessing
the strip still caused a crash. This commit fixes that by actually
initialising the invalid strip. Of course this still causes data loss, but
that already happened by opening & overwriting the file in Blender < 2.76.
aea4456101