Fixed installation problem

The Movie plugin requires both ffmpeg (or libav) and MuPDF.
Corrected conditional directives.

Change-Id: I96972cb5abbc98be01484c88e72b20763a6c53c3
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/76
Reviewed-by: Christian Felder <c.felder@fz-juelich.de>
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>