Actually ignore no-op `setGState` (PR 5192 followup)

The intention of PR 5192 was to avoid adding empty `setGState` ops to the operatorList. But the patch accidentally used `>=`, which means that it's not actually working as intended, since empty arrays always have `length === 0`.

src/core/evaluator.js

@@ -542,7 +542,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
         }
       }
       return promise.then(function () {
-        if (gStateObj.length >= 0) {
+        if (gStateObj.length > 0) {
           operatorList.addOp(OPS.setGState, [gStateObj]);
         }
       });