When no date, use now, instead of 0 (1970)

[積丹尼 Dan Jacobson]

When tramp is copying (from android (termux ssh)) and the file date is
(perhaps) not available, then maybe instead of using 0 (1970) as the date,
$ ls -l destination
  -rw-rw---- 1 jidanni jidanni 2310202 1970-01-01  P_20191224_094934_vHDR_On.jpg
  -rw-rw---- 1 jidanni jidanni 2079894 1970-01-01  P_20191227_101154_vHDR_On.jpg
  -rw-rw---- 1 jidanni jidanni 1685860 1970-01-01  P_20191227_102145_vHDR_On.jpg
  -rw-rw---- 1 jidanni jidanni 1095279 1970-01-01  P_20191227_102618_vHDR_On.jpg
  -rw-rw---- 1 jidanni jidanni  791235 1970-01-01  P_20191227_114225_vHDR_On.jpg
just use now, like plain cp(1) would.