config --replace-all: avoid extra line breaks

config --replace-all: avoid extra line breaks

When replacing multiple config entries at once, we did not re-set the
flag that indicates whether we need to insert a new-line before the new
entry. As a consequence, an extra new-line was inserted under certain
circumstances.

Signed-off-by: Johannes Schindelin <redacted>
Signed-off-by: Junio C Hamano <redacted>