log: Avoid buffer overflow

There was attempt to fix this in bb3a3cb, but it fixed only the case
when this value was actually provided by the token. When the token does
not support clock, it would print behind the "" buffer, causing random
constant string to be printed instead of the actual value, for example

	utcTime: ../common/attrs

This simplifies the long line for readability and prints additional
information about this value being unsupported by the token.

Signed-off-by: Jakub Jelen <jjelen@redhat.com>

p11-kit/log.c

@@ -731,7 +731,11 @@ log_token_info (p11_buffer *buf,
 		          (unsigned int)info->firmwareVersion.minor);
 		p11_buffer_add (buf, temp, -1);
 		p11_buffer_add (buf, "\n\tutcTime: ", -1);
-		p11_buffer_add (buf, (info->flags & CKF_CLOCK_ON_TOKEN) ? (const char*)info->utcTime : "", sizeof (info->utcTime));
+		if (info->flags & CKF_CLOCK_ON_TOKEN) {
+			p11_buffer_add (buf, (const char*)info->utcTime, sizeof (info->utcTime));
+		} else {
+			p11_buffer_add (buf, "(not supported)", -1);
+		}
 		p11_buffer_add (buf, "\n      }\n", -1);
 	}
 }