glr2.cc: fix when the stack is not expandable

* data/skeletons/glr2.cc (yyexpandGLRStackIfNeeded): Fix the
implementation when !YYSTACKEXPANDABLE.

data/skeletons/glr2.cc

@@ -1364,8 +1364,9 @@ class state_stack {
   }
  public:
 #else
-  bool yyexpandGLRStackIfNeeded() {
-    return yystateStack.spaceLeft() < YYHEADROOM;
+  bool yyexpandGLRStackIfNeeded ()
+  {
+    return spaceLeft () < YYHEADROOM;
   }
 #endif