Properly validate if argument parsing failed on -M.
Properly validate if argument parsing failed on -M.

* subversion/svnadmin/svnadmin.c
  (sub_main): Properly validate argument on --memory-cache-size and -M,


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1787023 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion