When loading Photoshop metadata from TIFF images, the size of the data
in the temp file was often incorrect.
This happens because run_mode is usually GIMP_RUN_INTERACTIVE when
run from within GIMP. In interactive mode, the last saved config values
take precedence over the ones set in the function call, which is not
what we want in this case.
We would prefer to use interactive here, because then we can show a
dialog with a list of unsupported Photoshop features that were found
inside the image.
For now, we will use GIMP_RUN_NONINTERACTIVE and accept that we can't
do that at this time. This way we will at least have the correct values
when processing the Photoshop data.