See Gentoo bug 251675. Upstream appears to be dead.

--- a/dog.c	2009-04-09 23:29:16.307661147 -0500
+++ b/dog.c	2009-04-09 23:30:11.353664890 -0500
@@ -552,7 +552,7 @@
 	
 	// strfry()
 #if ALLOW_STRFRY
-	if (opt_strfry) {
+	if (opt_strfry && str_len > 0) {
 		strfry(str);
 	}
 #endif