OZG-4097 send-attachment: Override contentLength

src/main/java/de/ozgcloud/nachrichten/postfach/osiv2/model/FileChunkInfo.java

@@ -25,6 +25,13 @@ public record FileChunkInfo(
 			public InputStream getInputStream() {
 				return new LimitedInputStream(fileInputStream, CHUNK_SIZE);
 			}
+
+			@Override
+			public long contentLength() {
+				return chunkIndex == upload.numberOfChunks() - 1
+						? upload.file().getSize() % CHUNK_SIZE
+						: CHUNK_SIZE;
+			}
 		};
 	}
 }