file: Don't show thumbnails for standard zoom level

For the first 2 levels of zoom, thumbnails aren't necessary as they don't
offer much useful information.

In this patch, we changed so that for the small and standard levels of icons,
we don't use thumbnails.

Fixes GNOME/nautilus#258
1 job for second-level-thumbnails in 7 minutes and 32 seconds (queued for 3 minutes and 27 seconds)
Status Job ID Name Coverage
  Test
passed #7913
test

00:07:32

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