evas: use SEQUENTIAL for decoding png file

Summary:
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

Subscribers: cedric, reviewers, committers

Tags: efl

Differential Revision: https://phab.enlightenment.org/D11783