gnutls_handshake fails after EAGAIN

[Vivek Dasmohapatra]

On Tue, 18 Aug 2009, Simon Josefsson wrote:

> Good to see it solved -- I closed the bug tracker for this.  Let me know
> if you think your patch is better, or if some other code improvement
> could be made here.

I don't think there's much to choose between them: it's a static function
called only from one place, so it doesn't matter much whether the change
is made in the caller or the callee.

Probably worth checking that other functions with a similar calling 
convention (once with data, then with NULL for each EAGAIN) are also 
handled suitably, since it's an easy mistake to make, and won't be picked
up if the tests use blocking push-pull functions.