Add fast-content-type fallback to all places
The G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE
attribute doesn't have to
be always set. The commit 0e597803 added the
G_FILE_ATTRIBUTE_STANDARD_FAST_CONTENT_TYPE
fallback inside the
NautilusFile
class, but not for other places. Let's fix this oversight.
Fixes: #2862 (closed)