bug fix, avoid segfault when indexing a vector with a nonexistant variable

ChangeLog

@@ -1,3 +1,8 @@
+2011-06-02  Robert Larice
+ * src/frontend/com_let.c :
+   bug fix, avoid segfault when indexing a vector with a nonexistant variable
+     let foo = thing[nonsuchthing]
+
 2011-06-02  Robert Larice
  * src/frontend/postcoms.c :
    bug fix, avoid $curplot (plot_names) being assembled from negative numbers

src/frontend/com_let.c

@@ -79,8 +79,18 @@ com_let(wordlist *wl)
 	    /* va, indexing */
 	    fake_wl.wl_word = s;
 	    nn = ft_getpnames(&fake_wl, TRUE);
+	    if (!nn) {
+		/* XXX error message */
+		tfree(p);
+		return;
+	    }
 	    t = ft_evaluate(nn);
-
+	    if (!t) {
+		fprintf(cp_err, "Error: Can't evaluate %s\n", s);
+		free_pnode(nn);
+		tfree(p);
+		return;
+	    }
 	    if (!isreal(t) || t->v_link2 || t->v_length != 1 || !t->v_realdata)
 	    {
 		fprintf(cp_err, "Error: index is not a scalar.\n");