Use Post Location when viewing map

Previously, we were using the current location, which may or may not
accurately represent the post location.
Catch null loc values when getting post from DB

We were just grabbing the lat/lng values set in the db and setting as
is. For posts without a location, this meant that we would set their
lat/lng to 0,0 which is a valid location.

We now check for null db column entries before setting the location
value for the post to prevent that.
Call getLocation only for posts without location

Post.isNew has a bug currently, which causes it to return
true for almost all posts (see #1463). Instead of prompting the
auto-location detection for isNew posts, so it only for posts that don't
have a location so we don't end up unnecessarily overriding things.

We will override this behavior soon to make the location setting
on-demand.