title: inventory.getPurchase() always return null although purchased already
body: <p>I working with a sample of in-ap purchase. My application have 2 buttons, first button was disable by default, click on second button will purchase and enable the first button. The purchase button work correct but after purchase, I've check the inventory but it's always return null, it's mean I haven't purchased yet.</p>
  
  <p>Here is the source code:</p>
  
  <p>Setup:</p>
  
  <pre><code>@Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      buyButton = (Button) findViewById(R.id.buyButton);
      clickButton = (Button) findViewById(R.id.clickButton);
      clickButton.setEnabled(false);
      String base64EncodedPublicKey = "key";
      mHelper = new IabHelper(this, base64EncodedPublicKey);
  
      mHelper.startSetup(new IabHelper.OnIabSetupFinishedListener() {
          public void onIabSetupFinished(IabResult result) {
              if (!result.isSuccess()) {
                  Log.d(TAG, "In-app Billing setup failed: " + result);
              } else {
                  Log.d(TAG, "In-app Billing is set up OK");
              }
              // Query to detect user was buy this item or not
              mHelper.queryInventoryAsync(mReceivedInventoryListener);
          }
      });
  
      buyButton.setOnClickListener(new OnClickListener() {
  
          @Override
          public void onClick(View v) {
              if (clickButton.isEnabled()) {
                  mHelper.queryInventoryAsync(mReceivedInventoryListener);
              } else {
                  buyClick(v);
              }
          }
      });
  }
  </code></pre>
  
  <p>The buy item click:</p>
  
  <pre><code>public void buyClick(View view) {
      mHelper.launchPurchaseFlow(this, ITEM_SKU, 10001,
              mPurchaseFinishedListener, "");
  }
  
  IabHelper.OnIabPurchaseFinishedListener mPurchaseFinishedListener = new IabHelper.OnIabPurchaseFinishedListener() {
      public void onIabPurchaseFinished(IabResult result, Purchase purchase) {
          if (result.isFailure()) {
              // Handle error
              return;
          } else if (purchase.getSku().equals(ITEM_SKU)) {
              // consumeItem();
              // buyButton.setEnabled(false);
              mHelper.consumeAsync(purchase, mConsumeFinishedListener);
          }
  
      }
  };
  </code></pre>
  
  <p>The listener:</p>
  
  <pre><code>IabHelper.QueryInventoryFinishedListener mReceivedInventoryListener = new IabHelper.QueryInventoryFinishedListener() {
      public void onQueryInventoryFinished(IabResult result,
              Inventory inventory) {
  
          if (result.isFailure()) {
              Toast.makeText(getApplicationContext(),
                      "Query Inventory Error!", Toast.LENGTH_SHORT).show();
              // Handle failure
          } else {
              Toast.makeText(getApplicationContext(),
                      "Query Inventory Success!", Toast.LENGTH_SHORT).show();
              // mHelper.consumeAsync(inventory.getPurchase(ITEM_SKU),
              // mConsumeFinishedListener);
              // if (inventory.hasPurchase(ITEM_SKU)) {
              // clickButton.setEnabled(true);
              // }
              Purchase item = inventory.getPurchase(ITEM_SKU);
              if (item != null) {
                  clickButton.setEnabled(true);
              } else {
                  Toast.makeText(getApplicationContext(),
                          "This item was not buy yet!", Toast.LENGTH_SHORT)
                          .show();
              }
          }
      }
  };
  IabHelper.OnConsumeFinishedListener mConsumeFinishedListener = new IabHelper.OnConsumeFinishedListener() {
      public void onConsumeFinished(Purchase purchase, IabResult result) {
  
          if (result.isSuccess()) {
              Toast.makeText(getApplicationContext(), "Consume done!",
                      Toast.LENGTH_SHORT).show();
              clickButton.setEnabled(true);
          } else {
              Toast.makeText(getApplicationContext(), "Consume Error!",
                      Toast.LENGTH_SHORT).show();
              // handle error
          }
      }
  };
  </code></pre>
  
  <p>When first click on buy button, it's show the payment dialog, after make payment success, the clickButton was enable.</p>
  
  <p>But when I click on the buyButton at the second times, it's go to inventory but the <strong>inventory.getPurchase(ITEM_SKU)</strong> always return null.</p>
  
  <p>Any idea?</p>
  
  <p>Thank you!</p>