net/http: map FS Open errors just like Dir

When an http.FileServer is given a path like file1/file2 where file1
exists but file2 does not, the proper HTTP status should be
NotFound. Some OSes return a "not a directory" error instead, so this
must be mapped to NotFound.

That mapping was already being done for the Dir FileSystem
implementation, as discussed in #18984. But it wasn't for the
FS implementation.

This CL does the same mapping for FS, by generalizing the function
that did it for Dir.

Fixes #49552

Change-Id: I61d6aa8ef101158e9674707d44e653f5dedbd040
Reviewed-on: https://go-review.googlesource.com/c/go/+/376874
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

0 files changed, 0 insertions, 0 deletions