fix #7343

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/opt/opt_parse.cpp

@@ -69,7 +69,7 @@ class opt_stream_buffer {
 bool opt_stream_buffer::parse_token(char const* token) {
     skip_whitespace();
     char const* t = token;
-    while (ch() == *t) {
+    while (*t && ch() == *t) {
         next();
         ++t;
     }