[expr.pre] Clarify note on pointer subtraction

Author: vasama

source/expressions.tex

@@ -6283,13 +6283,13 @@
 array elements $i$ and $j$
 of the same array object \tcode{x},
 the expression \tcode{P - Q} has the value $i - j$.
-\item Otherwise, the behavior is undefined.
 \begin{note}
 If the value $i - j$
 is not in the range of representable values
 of type \tcode{std::ptrdiff_t},
-the behavior is undefined.
+the behavior is undefined\iref{expr.pre}.
 \end{note}
+\item Otherwise, the behavior is undefined.
 \end{itemize}
 
 \pnum