Print call stack if an error occurs in a user-defined function.

src/userfns.c

@@ -316,7 +316,11 @@ int CallUserFunc(char const *name, int nargs, ParsePtr p)
     /* Skip the opening bracket, if there's one */
     while (isempty(*s)) s++;
     if (*s == BEG_OF_EXPR) s++;
+    push_call(f->filename, f->name, f->lineno);
     h = Evaluate(&s, f->locals, p);
+    if (h == OK) {
+        pop_call();
+    }
     f->IsActive = 0;
     DestroyLocalVals(f);
     if (DebugFlag &DB_PRTEXPR) {