add to lower case to make asset loading case insensitive (#1427)

This should fix bug #1425

Author: Archina

crates/bevy_asset/src/asset_server.rs

@@ -154,12 +154,13 @@ impl AssetServer {
                 extensions: Vec::new(),
             })?
             .to_str()
+            .map(|s| s.to_lowercase())
             .ok_or(AssetServerError::MissingAssetLoader {
                 extensions: Vec::new(),
             })?;
 
         let mut exts = Vec::new();
-        let mut ext = s;
+        let mut ext = s.as_str();
         while let Some(idx) = ext.find('.') {
             ext = &ext[idx + 1..];
             exts.push(ext);
@@ -552,6 +553,13 @@ mod test {
         assert_eq!(t.unwrap().extensions()[0], "png");
     }
 
+    #[test]
+    fn case_insensitive_extensions() {
+        let asset_server = setup();
+        let t = asset_server.get_path_asset_loader("test.PNG");
+        assert_eq!(t.unwrap().extensions()[0], "png");
+    }
+
     #[test]
     fn no_loader() {
         let asset_server = setup();