Fixing AssetService - after Falk broke it.

Author: FalkWolsky

server/api-service/lowcoder-domain/src/main/java/org/lowcoder/domain/asset/service/AssetServiceImpl.java

@@ -61,7 +61,7 @@ public Mono<Asset> upload(Part filePart, int maxFileSizeKB, boolean isThumbnail)
 
         // The reason we restrict file types here is to avoid having to deal with dangerous image types such as SVG,
         // which can have arbitrary HTML/JS inside of them.
-            
+        final MediaType contentType = filePart.headers().getContentType();
         if (contentType == null || !ALLOWED_CONTENT_TYPES.contains(contentType)) {
             return Mono.error(new BizException(BizError.INVALID_PARAMETER, "INCORRECT_IMAGE_TYPE"));
         }