Bug 1224013 part 2 - Move leading fix to ruby base container. r=dholbert

Per spec, the additional leading is added on side of ruby base container, not
ruby container. This could lead to some trivial behavior changes on edge cases.

layout/generic/nsRubyBaseContainerFrame.cpp

@@ -323,6 +323,9 @@ nsRubyBaseContainerFrame::Reflow(nsPresContext* aPresContext,
     textContainers[i]->MoveOverflowToChildList();
   }
 
+  // Clear leadings
+  mBStartLeading = mBEndLeading = 0;
+
   WritingMode lineWM = aReflowState.mLineLayout->GetWritingMode();
   LogicalSize availSize(lineWM, aReflowState.AvailableISize(),
                         aReflowState.AvailableBSize());