Refactor code for <img> size calculation during attach

Source/core/html/HTMLImageElement.cpp

Index: Source/core/html/HTMLImageElement.cpp
diff --git a/Source/core/html/HTMLImageElement.cpp b/Source/core/html/HTMLImageElement.cpp
index e96f979fa7d6d19845908b8932b4e39f0182ed6b..2303be26fa356cd392a94ab2186aed9f010547e1 100644
--- a/Source/core/html/HTMLImageElement.cpp
+++ b/Source/core/html/HTMLImageElement.cpp
@@ -165,12 +165,14 @@ void HTMLImageElement::attach(const AttachContext& context)
         RenderImageResource* renderImageResource = renderImage->imageResource();
         if (renderImageResource->hasImage())
             return;
-        renderImageResource->setCachedImage(m_imageLoader.image());
 
         // If we have no image at all because we have no src attribute, set
         // image height and width for the alt text instead.
         if (!m_imageLoader.image() && !renderImageResource->cachedImage())
             renderImage->setImageSizeForAltText();
+        else
+            renderImageResource->setCachedImage(m_imageLoader.image());
+
     }
 }