The function emitted two consecutive 8-byte position blocks instead of
one, producing a frame 8 bytes longer than the documented layout. When
a caller passed lastModified, the firmware parsed the duplicated second
lat as the timestamp, giving wildly wrong "last seen" values on
imported contacts.
Delete the unconditional first block; keep the conditional block that
correctly skips the optional tail when neither location nor
lastModified is set, zero-fills position slots when only lastModified
is present, and appends the optional timestamp.
Adds test/connector/build_update_contact_path_frame_test.dart with
five cases covering all four optional-tail combinations plus the
fixed-point lat/lon encoding.
Fixes#427