[conv.lval] Make note and generalize comment on UB

Author: eisenwave

source/expressions.tex

@@ -675,9 +675,10 @@
 
 \item Otherwise, the object indicated by the glvalue is read\iref{defns.access},
 and the value contained in the object is the prvalue result.
-If the result is an erroneous value\iref{basic.indet} and
-the bits in the value representation are not valid for the object's type,
+\begin{note}
+If the bits in the value representation are not valid for the object's type,
 the behavior is undefined.
+\end{note}
 \end{itemize}
 
 \pnum