plugins/urandom: fix resource leak, found by Coverity Scan

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

plugins/urandom.c

@@ -108,6 +108,7 @@ static void setup(void *arg)
 			if (len > 0)
 				break;
 
+			close(fd);
 			free(rpi);
 			goto fallback;
 		}