修正 Raw 图片输出格式回退

忽略空值后再使用载荷级格式
补充空字符串和 null 回归测试

server-rs/crates/platform-image/src/vector_engine/raw_edit.rs

@@ -366,10 +366,16 @@ fn response_image_format(
 ) -> Result<(&'static str, &'static str), &'static str> {
     let Some(value) = entry
         .get("output_format")
-        .or_else(|| payload.get("output_format"))
         .and_then(Value::as_str)
         .map(str::trim)
         .filter(|value| !value.is_empty())
+        .or_else(|| {
+            payload
+                .get("output_format")
+                .and_then(Value::as_str)
+                .map(str::trim)
+                .filter(|value| !value.is_empty())
+        })
     else {
         return Err("上游响应缺少 output_format");
     };
@@ -455,6 +461,20 @@ mod tests {
             response_image_format(&json!({}), &json!({"output_format": "jpeg"})),
             Ok(("image/jpeg", "jpg"))
         );
+        assert_eq!(
+            response_image_format(
+                &json!({"output_format": "png"}),
+                &json!({"output_format": ""})
+            ),
+            Ok(("image/png", "png"))
+        );
+        assert_eq!(
+            response_image_format(
+                &json!({"output_format": "webp"}),
+                &json!({"output_format": null})
+            ),
+            Ok(("image/webp", "webp"))
+        );
         assert!(response_image_format(&json!({}), &json!({})).is_err());
         assert!(response_image_format(&json!({}), &json!({"output_format": "bmp"})).is_err());
     }