Fixed that return value of malloc was not checked.
Fixed wrong argument count (compilation failure) to base64_decode()
function.

Note:
- there is no test case for this fix as this code is never compiled
  into mysql clients/server;
- as this code is used for internal testing purposes only, no changelog
  entry needed.


mysys/base64.c:
  Fixed that return value of malloc was not checked.
  Fixed wrong argument count to base64_decode function.