[omemo] Remove needless stream.close()

This is only a BytesIO Object in memory, its becomes garbage collected
after the method ends anyway

Fixes #232

omemo/file_decryption.py

@@ -228,7 +228,7 @@ class Download:
         except Exception as error:
             log.exception('Error')
             errormsg = error
-        stream.close()
+
         return str(errormsg)
 
     def aes_decrypt(self, payload):