cli: sanitize tabs and newlines to spaces in notmuch search

cli: sanitize tabs and newlines to spaces in notmuch search

Sanitize tabs and newlines to spaces rather than question marks in
--output=summary --format=text output.

This will also hide any difference in unfolding a header that has been
folded with a tab. Our own header parser replaces tabs with spaces,
while gmime would retain the tab.