When confirm_margin() first sets the margin needed for the requested
line numbers, also then it needs to keep 'focusing' TRUE. Only when
actually toggling --linenumbers ON (from a zero margin to something)
should focusing be suppressed, in order to obtain smooth scrolling
when the cursor is pushed off-screen.
This fixes https://savannah.gnu.org/bugs/?62885.
Bug existed since version 4.4, since the search-at-startup feature
was introduced.
83629b9991