The base64 encoded data cannot included pad characters in the middle, so
we can stop the loop at the first sequence of pad characters. If the
sequence includes more than two pad characters, the encoding is invalid
and we can indicate failure.
If base64_encode() were to be used with a huge data array, the
previous version could have resulted in overwriting the allocated
buffer due to an integer overflow as pointed out in
http://www.freebsd.org/cgi/query-pr.cgi?pr=137484. However, there
are no know use cases in hostapd or wpa_supplicant that would do that.
Anyway, the recommended change looks reasonable and provides additional
protection should the base64_encode() function be used for something
else in the future.
