assrender: Fix mimetype detection
Previously gst_structure_has_name
was used to get a string to compare with supported mimetypes.
This is incorrect as above function returns a user defined structure name which is
not the structure mimetype value.
Up until now assrender
compared string containing the mimetype with GstTagImageInfo
string and failed each time.
I also moved the filename
existence check before the array iterations, as there is no point
spending time on iterating and comparing strings if we are going to reject the value due to missing
filename anyway.
Depends on: gst-plugins-good!858 (closed)