No point in storing empty EXIF/IPTC data on post meta table

[geminorum]

• Post meta tables are bloated with often not used EXIF/IPTC data for each image attachments.

• wp_read_image_metadata() generates aperture, credit, camera, caption, created_timestamp, copyright, focal_length, iso, shutter_speed, title, orientation, keywords. and the data often stored as empty key/value pairs on each attachment metadata.

• I see no problem on filling default/empty values upon retrieving the data.

• and mentioning the core currently has no way of using stored image_meta.