[fractal] delete temporary thumbnail file

[Christopher Davis <christopherdavis src gnome org>]

commit 9eb315a816bc93520091506369e04b940ee81bb8
Author: mairandomness <mairakodama gmail com>
Date:   Mon Feb 18 21:30:53 2019 -0500

    delete temporary thumbnail file

 fractal-matrix-api/src/backend/room.rs | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/fractal-matrix-api/src/backend/room.rs b/fractal-matrix-api/src/backend/room.rs
index de13b9b6..2349509d 100644
--- a/fractal-matrix-api/src/backend/room.rs
+++ b/fractal-matrix-api/src/backend/room.rs
@@ -490,6 +490,9 @@ pub fn attach_file(bk: &Backend, mut msg: Message) -> Result<(), Error> {
                     msg.extra_content = Some(serde_json::to_value(&extra_content).unwrap());
                 }
             }
+            if let Err(_e) = std::fs::remove_file(&thumb) {
+                error!("Can't remove thumbnail: {}", thumb);
+            }
         }
 
         match upload_file(&tk, &baseu, &fname) {