view,searchview: avoid smsg method calls when using SQLite/Xapian

view,searchview: avoid smsg method calls when using SQLite/Xapian

We already pre-populate the hashref when loading $smsg
(PublicInbox::SearchMsg) objects out of over.sqlite3 or Xapian,
so making expensive method calls isn't necessary in those cases.

We only need to use the method calls when SQLite or Xapian are
not available or are being populated (such as during indexing).