graphics/zathura-pdf-mupdf: Add missing LIB_DEPENDS

Add missing jbig2dec and openjpeg to LIB_DEPENDS, registering them
as run-time dependencies.

Without this change, both packages are removed during pkg autoremove,
resulting in the inability to open PDF files.

PR: 203850
Submitted by: Zsolt Udvari <udvzsolt gmail com> (maintainer)
MFH: 2015Q4