Remove useless null checks from Node::document() call sites

Source/core/editing/FrameSelection.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 224 matching lines @@
 
     if (!m_frame) {
         m_selection = s;
         return;
     }
 
     // <http://bugs.webkit.org/show_bug.cgi?id=23464>: Infinite recursion at FrameSelection::setSelection
     // if document->frame() == m_frame we can get into an infinite loop
     if (s.base().anchorNode()) {
         Document* document = s.base().anchorNode()->document();
-        if (document && document->frame() && document->frame() != m_frame && document != m_frame->document()) {
+        if (document->frame() && document->frame() != m_frame && document != m_frame->document()) {
             RefPtr<Frame> guard = document->frame();
             document->frame()->selection()->setSelection(s, options, align, granularity);
             // It's possible that during the above set selection, this FrameSelection has been modified by
             // selectFrameElementInParentIfFullySelected, but that the selection is no longer valid since
             // the frame is about to be destroyed. If this is the case, clear our selection.
             if (guard->hasOneRef() && !m_selection.isNonOrphanedCaretOrRange())
                 clear();
             return;
         }
     }
@@ skipping 1675 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const WebCore::FrameSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif