fixup: herb suggestion for variable name

Author: notadragon

source/ub.tex

@@ -1674,7 +1674,7 @@
 {
   X* px = &g();
   px->~X();
-  int p = px->i;    // undefined behavior
+  int j = px->i;    // undefined behavior
 }
 \end{codeblock}
 \end{example}