Clean up XFA code which causes warnings

xfa/fwl/lightwidget/cfwl_theme.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "xfa/fwl/lightwidget/cfwl_theme.h"
 
 #include <algorithm>
 
@@ skipping 38 matching lines @@
   return !!GetTheme(pWidget);
 }
 
 uint32_t CFWL_Theme::GetThemeID(IFWL_Widget* pWidget) {
   return GetTheme(pWidget)->GetThemeID(pWidget);
 }
 
 uint32_t CFWL_Theme::SetThemeID(IFWL_Widget* pWidget,
                                 uint32_t dwThemeID,
                                 FX_BOOL bChildren) {
-  uint32_t dwID;
+  uint32_t dwID = 0;
   for (const auto& pTheme : m_ThemesArray) {
     dwID = pTheme->GetThemeID(pWidget);
     pTheme->SetThemeID(pWidget, dwThemeID, FALSE);
   }
   return dwID;
 }
 
 FWL_Error CFWL_Theme::GetThemeMatrix(IFWL_Widget* pWidget, CFX_Matrix& matrix) {
   return FWL_Error::Succeeded;
 }
@@ skipping 61 matching lines @@
   return FWL_Error::Succeeded;
 }
 
 CFWL_WidgetTP* CFWL_Theme::GetTheme(IFWL_Widget* pWidget) {
   for (const auto& pTheme : m_ThemesArray) {
     if (pTheme->IsValidWidget(pWidget))
       return pTheme.get();
   }
   return nullptr;
 }