add overrun check to SEE

src/fh_see.c

@@ -15,6 +15,12 @@ static void show_word(struct fh_thread_s *fh, const struct fh_word_s *w)
       while (1) {
         // make sure it's aligned
         execptr = WORDALIGNED(execptr);
+        
+        if (execptr == 0 || execptr > fh->here) {
+          LOGE("Exec overrun without ENDWORD!");
+          break;
+        }
+        
         FHPRINT("0x%08x: ", execptr);
         const struct fh_instruction_s *instr = fh_instr_at(fh, execptr);
         if (!instr) {