More consistent handling of non-Unicode file names (should be rare)

src/snapshot_middleware/json_model.rs

@@ -9,7 +9,10 @@ use crate::{
     snapshot::InstanceSnapshot,
 };
 
-use super::middleware::{SnapshotFileResult, SnapshotInstanceResult, SnapshotMiddleware};
+use super::{
+    error::SnapshotError,
+    middleware::{SnapshotFileResult, SnapshotInstanceResult, SnapshotMiddleware},
+};
 
 pub struct SnapshotJsonModel;
 
@@ -22,7 +25,12 @@ impl SnapshotMiddleware for SnapshotJsonModel {
             return Ok(None);
         }
 
-        let file_name = entry.path().file_name().unwrap().to_string_lossy();
+        let file_name = entry
+            .path()
+            .file_name()
+            .unwrap()
+            .to_str()
+            .ok_or_else(|| SnapshotError::file_name_bad_unicode(entry.path()))?;
 
         let instance_name = match match_trailing(&file_name, ".model.json") {
             Some(name) => name.to_owned(),