gpg: Initialize a parameter to silence valgrind.

* g10/keygen.c (read_parameter_file): Initialize nline.
* g10/textfilter.c (copy_clearsig_text): Initialize bufsize.

In iobuf_read_line the parameter to pass and return the current buffer
length is controlled by the buffer parameter. Thus there should be no
problem because the assert call check s buffer first. For yet unknown
reasons when using the standard GNU libc assert valgrind complains
about an uninitialized variable. That does not happen with our
log_assert. Tested with gcc 8.3.0 and valgrind 3.14.0.