[Perl/perl5] 153764: time64.c: avoid 'uninit' compiler warning

[iabyn via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 153764ac87c44440fea60466e8f718671117bac2
      
https://github.com/Perl/perl5/commit/153764ac87c44440fea60466e8f718671117bac2
  Author: David Mitchell <da...@iabyn.com>
  Date:   2020-12-03 (Thu, 03 Dec 2020)

  Changed paths:
    M time64.c

  Log Message:
  -----------
  time64.c: avoid 'uninit' compiler warning

clang isn't smart enough to recognise the pattern:

    if (foo) { ...} { else orig_year = ... }
    ...
    if (!foo) { ... use orig_year .. }

So just unconditionally initialise orig_year.