Add missing false return type in hash_file documentation (#4671)

Author: cedric-anne

reference/hash/functions/hash-file.xml

@@ -66,7 +66,7 @@
   <para>
    Returns a string containing the calculated message digest as lowercase hexits
    unless <parameter>binary</parameter> is set to true in which case the raw
-   binary representation of the message digest is returned.
+   binary representation of the message digest is returned, &return.falseforfailure;.
   </para>
  </refsect1>