ssh signing: signal an error with a negative return value

The other backend for the sign_buffer() function followed our usual
"an error is signalled with a negative return" convention, but the
SSH signer did not.  Even though we already fixed the caller that
assumed only a negative return value is an error, tighten the callee
to signal an error with a negative return as well.  This way, the
callees will be strict on what they produce, while the callers will
be lenient in what they accept.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

gpg-interface.c

@@ -1088,7 +1088,7 @@ static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
 		if (strstr(signer_stderr.buf, "usage:"))
 			error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));
 
-		error("%s", signer_stderr.buf);
+		ret = error("%s", signer_stderr.buf);
 		goto out;
 	}