Use application/octet-stream as default type in TemporaryStorageProvider

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/provider/TemporaryStorageProvider.java

@@ -180,7 +180,7 @@ public class TemporaryStorageProvider extends ContentProvider {
                 cursor.close();
             }
         }
-        return "*/*";
+        return "application/octet-stream";
     }
 
     @Override