pass omitFilename to stop sending filename=undefined

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/ContentMessages.js

@@ -243,6 +243,7 @@ function uploadFile(matrixClient, roomId, file, progressHandler) {
             const blob = new Blob([encryptResult.data]);
             return matrixClient.uploadContent(blob, {
                 progressHandler: progressHandler,
+                omitFilename: true,
             }).then(function(url) {
                 // If the attachment is encrypted then bundle the URL along
                 // with the information needed to decrypt the attachment and