Fix timeout on empty socket in HTTPClient

[annda]

feof() sometimes hangs if nothing has been written yet, so we skip the check initially.

See php/php-src#3729

[splitbrain]

Some additional info: we had this problem on only one machine with PHP 7.0 when trying to fetch data from a github URL. It may or may not be related to the issue mentioned above. Some additional testing on different PHP versions would be helpful to see if we can pinpoint if feof always hangs on certain PHP releases or if there are other circumstances involved.

The fix suggested above is slightly sub-optimal because it will result in hanging until a timeout on sockets that get immeadiately closed after opening for some reason.

This may or may not be slightly related to #3474