Adding check for null document. Prevents crash described in bug 20677.

r=brendan@mozilla.org

layout/generic/nsTextFrame.cpp

@@ -2819,6 +2819,9 @@ nsTextFrame::Reflow(nsIPresContext* aPresContext,
   // Setup text transformer to transform this frames text content
   nsCOMPtr<nsIDocument> doc;
   mContent->GetDocument(*getter_AddRefs(doc));
+  if (NS_WARN_IF_FALSE(doc, "Content has no document.")) { 
+    return NS_ERROR_FAILURE; 
+  }
   nsCOMPtr<nsILineBreaker> lb;
   doc->GetLineBreaker(getter_AddRefs(lb));
   nsTextTransformer tx(lb, nsnull);

layout/html/base/src/nsTextFrame.cpp

@@ -2819,6 +2819,9 @@ nsTextFrame::Reflow(nsIPresContext* aPresContext,
   // Setup text transformer to transform this frames text content
   nsCOMPtr<nsIDocument> doc;
   mContent->GetDocument(*getter_AddRefs(doc));
+  if (NS_WARN_IF_FALSE(doc, "Content has no document.")) { 
+    return NS_ERROR_FAILURE; 
+  }
   nsCOMPtr<nsILineBreaker> lb;
   doc->GetLineBreaker(getter_AddRefs(lb));
   nsTextTransformer tx(lb, nsnull);