prevent negative focus distance when reading Olympus exifs; a quick fix for #9895

there is still a bit of vulnerability in our code as it decides on availability
of exif data (exif_inited) based on some ad-hoc checks which might fail
lua : add float-typed preferences
Updated Dutch translation
Merge pull request #534 from MRIG/master

Updated Dutch translation
Avoid flickering of stars and drop shadow for zoom == 1

This commit avoids the nasty flickring of the stars and the drop shadow
when scrolling through images at zoom level 1 or full preview (z)
introspection: new helpers to access array/struct

WARNING: this changes dt_introspection_access_array()
TODO: support unions