* src/visibility.c (gpgrt_pending, gpgrt_pending_unlocked): New.
* src/estream.c (_gpgrt_pending, _gpgrt_pending_unlocked): New.
(check_pending): new.
(check_pending_fbf, check_pending_nbf): New.
(es_func_mem_read, es_func_fd_read, es_func_w32_read)
(es_func_fp_read, es_fill): Take care of the special 0 value for SIZE.