Fix error when displaying custom date format in details view (issue #389)

Fixes a bug caused by use of a shared static "struct tm" by taking a copy
of the struct to pass to exo_strdup_strftime rather than passing a pointer
to the shared struct.
2 jobs for !33 with fix-custom-format-date in 6 minutes and 34 seconds (queued for 6 seconds)
merge request