debugging aid to uc_dstr_destroy too

src/dstr.c

@@ -14,6 +14,13 @@ void uc_dstr_init(struct DStr *str)
 
 void uc_dstr_destroy(struct DStr *str)
 {
+#ifdef DEBUG
+    if (str->str) {
+        memset(str->str, 0xcc, str->allocated);
+    }
+    str->len = -1;
+    str->allocated = -1;
+#endif
     free(str->str);
 }