fix: flickering

it does still reload the image,
but at least it doesn't flicker while doing so

this also exposes a problem with the error reporting,
since with so many error-reporting operations going on,
the errors that do happen are most often immediately cleared.

src/app/mod.rs

@@ -87,9 +87,13 @@ impl State {
                 self.error = result.as_ref().err().map(|e| e.to_string());
 
                 if let Ok((path, handle)) = result {
-                    self.images
-                        .entry(path)
-                        .and_modify(|e| *e = MaybeImage::Loaded(handle));
+                    let entry = self.images.entry(path).or_default();
+
+                    if matches!(entry, MaybeImage::Loaded(_)) {
+                        self.error = Some("tried to load already-loaded image!".into())
+                    } else {
+                        *entry = MaybeImage::Loaded(handle)
+                    }
                 }
             }