Handle missing glyphs when adjusting spacing in SimpleShaper

Source/platform/fonts/shaping/SimpleShaper.cpp

 /*
  * Copyright (C) 2003, 2006, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Holger Hans Peter Freyther
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 189 matching lines @@
 
         Glyph glyph = glyphData.glyph;
         const SimpleFontData* fontData = glyphData.fontData;
         ASSERT(fontData);
 
         if (m_fallbackFonts && lastFontData != fontData && width) {
             lastFontData = fontData;
             cacheFallbackFont(fontData, primaryFont);
         }
 
-        if (hasExtraSpacing)
+        if (hasExtraSpacing && width)

[pdr., 2014/10/13 23:53:30]

(Maybe as a followup) Can you add a bool to better describe what's going on when
width=0? This seems to have been first added back in
https://chromium.googlesource.com/chromium/blink/+/4a2a3ba905642998075cf4b161...
and it'll be easy to make this mistake again.

             width = adjustSpacing(width, charData, *fontData, glyphBuffer);

[pdr., 2014/10/13 23:53:30]

Does it make sense to check for width in adjustSpacing after this patch? I don't
fully understand the comment in adjustSpacing in the context of this patch.

 
         if (m_bounds)
             updateGlyphBounds(glyphData, width, !charData.characterOffset);
 
         if (m_forTextEmphasis && !Character::canReceiveTextEmphasis(charData.character))
             glyph = 0;
 
         // Advance past the character we just dealt with.
         textIterator.advance(charData.clusterLength);
         m_runWidthSoFar += width;
@@ skipping 32 matching lines @@
     float initialWidth = m_runWidthSoFar;
 
     if (!advance(m_currentCharacter + 1))
         return false;
 
     width = m_runWidthSoFar - initialWidth;
     return true;
 }
 
 } // namespace blink