Added a control statement to avoid doing work that will lead nowhere.

layout/mathml/base/src/nsMathMLmiFrame.cpp

@@ -123,7 +123,8 @@ nsMathMLmiFrame::SetInitialChildList(nsIPresContext& aPresContext,
 
   // Insert a new pseudo frame between our children and us, i.e., the new frame
   // becomes our sole child, and our children become children of the new frame.
-
+  nsIFrame* firstChild = mFrames.FirstChild();
+  if (firstChild) {
     // Get a pseudo style context for the appropriate style font
     // XXX how important is the PseudoStyleContext?
     nsAutoString fontStyle = (1 == aLength) 
@@ -143,18 +144,17 @@ nsMathMLmiFrame::SetInitialChildList(nsIPresContext& aPresContext,
       newFrame->Init(aPresContext, mContent, this, newStyleContext, nsnull);
     
       // our children become children of the new frame
-    nsIFrame* firstFrame = mFrames.FirstChild();
+      nsIFrame* childFrame = firstChild;
-    nsIFrame* childFrame = firstFrame;
+      while (childFrame) {
-    while (nsnull != childFrame) {
         childFrame->SetParent(newFrame);
         aPresContext.ReParentStyleContext(childFrame, newStyleContext);
         childFrame->GetNextSibling(&childFrame);
       }
-    newFrame->SetInitialChildList(aPresContext, nsnull, firstFrame);
+      newFrame->SetInitialChildList(aPresContext, nsnull, firstChild);
     
       // the new frame becomes our sole child
       mFrames.SetFrames(newFrame);
     }
-
+  }
   return rv;
 }