Harmonize index entries for 'null pointer value'. [reported upstream: cplusplus#1487]

Author: Eelis

source/basic.tex

@@ -4013,7 +4013,8 @@
 \item
 a \defn{pointer past the end of} an object (\ref{expr.add}), or
 \item
-the \defn{null pointer value} (\ref{conv.ptr}) for that type, or
+\indextext{null pointer value|see{value, null pointer}}
+the \defnx{null pointer value}{value!null pointer} (\ref{conv.ptr}) for that type, or
 \item
 an \defn{invalid pointer value}.
 \end{itemize}

source/conversions.tex

@@ -491,12 +491,11 @@
 \indextext{conversion!pointer}%
 \indextext{pointer!zero}%
 \indextext{constant!null pointer}%
-\indextext{value!null pointer}%
 A \term{null pointer constant} is an integer literal~(\ref{lex.icon}) with
 value zero
 or a prvalue of type \tcode{std::nullptr_t}. A null pointer constant can be
 converted to a pointer type; the
-result is the \term{null pointer value} of that type and is
+result is the \defnx{null pointer value}{value!null pointer} of that type and is
 distinguishable from every other value of
 object pointer or function pointer
 type.