part file needs to have .part extension

lib/private/connector/sabre/file.php

@@ -86,7 +86,7 @@ class OC_Connector_Sabre_File extends OC_Connector_Sabre_Node implements Sabre_D
 		// root folder because we can't create new files in /shared
 		// we extend the name with a random number to avoid overwriting a existing file
 		if (dirname($partpath) === 'Shared') {
-			$partpath = pathinfo($partpath, PATHINFO_FILENAME) . rand();
+			$partpath = pathinfo($partpath, PATHINFO_FILENAME) . rand() . '.part';
 		}
 
 		try {