Merge #1190: disable previous button if device processing

f457dd447cd4af89aace9f56e085073590dde8e5 installer: at descriptor registartion step, disable previous button if device processing (pythcoiner)

Pull request description:

  This PR diasable the previous button  at the descriptor registration step if a device is still processing, avoiding issues like #1158.
  The other way around can be to reset the state of `self.processing` if user go back, but look less clean to me.

  closes #1158

ACKs for top commit:
  edouardparis:
    utACK f457dd447cd4af89aace9f56e085073590dde8e5

Tree-SHA512: 7fee81b17d72f88eb1a673e2875ec9998e1ec7567afa1b487ca07b3d95c8fd1c161159660e37a2e1505b871ce2bf9286a75e5c055f777844062a78e0a08bc695

gui/src/installer/view.rs

@@ -750,7 +750,11 @@ pub fn register_descriptor<'a>(
             })
             .spacing(50),
         true,
-        Some(Message::Previous),
+        if !processing {
+        Some(Message::Previous)
+        } else {
+            None
+        }
     )
 }