dns: Fix bug in error handling when talking to script

dns: Fix bug in error handling when talking to script

Comparing the result of read/write to a size_t value
is dangerous C. Since ssize_t and size_t have the same
size ssize_t is promoted to size_t, so -1 becomes
size_t max value and is not smaller than the expected
length.

Make sure to compare ssize_t to ssize_t to avoid any
suprises.

Change-Id: Ic395b6d1dce510bb4b499c5beba61f033a2a860b
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Heiko Hund <heiko@openvpn.net>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1208
Message-Id: <20250924121901.13532-1-gert@greenie.muc.de>
URL: https://sourceforge.net/p/openvpn/mailman/message/59238099/
Signed-off-by: Gert Doering <gert@greenie.muc.de>