gitk: Don't clobber "Remember this view" setting

gitk: Don't clobber "Remember this view" setting

In the View → Edit View... dialog, the "Remember this view" option
always starts out unset.  Using the dialog to change an existing view
and ignoring the parts of the dialog that aren’t relevant results in
both the old and new versions of the view being lost.

The cause: right after newviewopts($curview,perm) is set to an
appropriate value, decode_view_opts is clobbering it with the default
value.  If that call is moved a little earlier, the "Remember this
view" option gets properly set to its previous value, fixing the
problem.

Reported-by: Steve Cotton <steve0001@s.cotton.clara.co.uk>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>