[class.protected] Add missing full stop at end of sentence. (#1614)

Author: Eelis

source/access.tex

@@ -855,7 +855,7 @@
 \pnum
 An additional access check beyond those described earlier in Clause~\ref{class.access}
 is applied when a non-static data member or non-static member function is a
-protected member of its naming class~(\ref{class.access.base})\footnote{This
+protected member of its naming class~(\ref{class.access.base}).\footnote{This
 additional check does not apply to other members,
 e.g., static data members or enumerator member constants.}
 As described earlier, access to a protected member is granted because the