evas: use SEQUENTIAL for decoding png file
There was a mistake caused by "2a0eeba evas: fix png regression issue".
The flag is_for_data was close_file before this commit.
_evas_image_load_file_internal_head_png closes file if it is called only for
header. So the close_file does not mean is_for_data.
This patch is changing is_for_data to is_for_head, and make
_evas_image_load_file_internal_head_png use EINA_FILE_SEQUENTIAL
for data decoding.
Reviewers: Hermet, jsuya, herb, raster
Reviewed By: raster
Differential Revision: https://phab.enlightenment.org/D11783