Added checks for null objects so printing would work.

widget/src/windows/nsButton.cpp

@@ -79,6 +79,9 @@ nsresult nsButton::QueryInterface(const nsIID& aIID, void** aInstancePtr)
 //-------------------------------------------------------------------------
 NS_METHOD nsButton::SetLabel(const nsString& aText)
 {
+  if (NULL == mWnd) {
+    return NS_ERROR_FAILURE;
+  }
   NS_ALLOC_STR_BUF(label, aText, 256);
   VERIFY(::SetWindowText(mWnd, label));
   NS_FREE_STR_BUF(label);

widget/src/windows/nsLabel.cpp

@@ -196,8 +196,12 @@ NS_METHOD nsLabel::GetBounds(nsRect &aRect)
 //-------------------------------------------------------------------------
 NS_METHOD nsLabel::GetPreferredSize(PRInt32& aWidth, PRInt32& aHeight)
 {
+  if (nsnull == mContext) {
+    return NS_ERROR_FAILURE;
+  }
   //nsIFontMetrics * fm = GetFont();;
  // mDeviceContext->GetMetricsFor(mFont, &fm);
+
   nsIFontMetrics* metrics;
   mContext->GetMetricsFor(*mFont, metrics);
 

widget/src/windows/nsWindow.cpp

@@ -927,6 +927,10 @@ nsIFontMetrics* nsWindow::GetFont(void)
 //-------------------------------------------------------------------------
 NS_METHOD nsWindow::SetFont(const nsFont &aFont)
 {
+    if (nsnull == mContext) {
+      return NS_ERROR_FAILURE;
+    }
+
     nsIFontMetrics* metrics;
     mContext->GetMetricsFor(aFont, metrics);
     nsFontHandle  fontHandle;