Fix composite key computation for BytesIO

In case a keyfile as BytesIO has been read before, the
next read will be empty. We need to ensure that we
are reading the data from the beginning.

Add seek to start to fix it.

Author: janbrummer

pykeepass/kdbx_parsing/common.py

@@ -128,6 +128,7 @@ def compute_key_composite(password=None, keyfile=None):
     # hash the keyfile
     if keyfile:
         if hasattr(keyfile, "read"):
+            keyfile.seek(0)
             keyfile_bytes = keyfile.read()
         else:
             with open(keyfile, 'rb') as f: