Fix false positives in message view tests.
Fix false positives in message view tests.

The `assert_message_groups_list_equal` and
`assert_message_list_equal` helpers were
always returning `true`, as they were doing
a bogus traversal of the data structures and
always comparing empty arrays, even when there
was real data.

To prevent this pitfall in the future, we assert
that the extracted data is truth-y, and for the
empty cases we just directly assert deep equality
to `[]`.

rht/zulip,rishig/zulip,brainwane/zulip,rishig/zulip,showell/zulip,kou/zulip,punchagan/zulip,showell/zulip,dhcrzf/zulip,andersk/zulip,synicalsyntax/zulip,tommyip/zulip,andersk/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,shubhamdhama/zulip,showell/zulip,tommyip/zulip,punchagan/zulip,brainwane/zulip,rishig/zulip,hackerkid/zulip,synicalsyntax/zulip,rht/zulip,andersk/zulip,showell/zulip,rht/zulip,dhcrzf/zulip,tommyip/zulip,synicalsyntax/zulip,timabbott/zulip,rht/zulip,zulip/zulip,tommyip/zulip,rht/zulip,shubhamdhama/zulip,kou/zulip,dhcrzf/zulip,dhcrzf/zulip,eeshangarg/zulip,timabbott/zulip,punchagan/zulip,eeshangarg/zulip,tommyip/zulip,hackerkid/zulip,rishig/zulip,brainwane/zulip,andersk/zulip,rht/zulip,synicalsyntax/zulip,synicalsyntax/zulip,timabbott/zulip,hackerkid/zulip,kou/zulip,showell/zulip,dhcrzf/zulip,kou/zulip,zulip/zulip,zulip/zulip,hackerkid/zulip,synicalsyntax/zulip,brainwane/zulip,shubhamdhama/zulip,punchagan/zulip,eeshangarg/zulip,andersk/zulip,punchagan/zulip,shubhamdhama/zulip,brainwane/zulip,zulip/zulip,rishig/zulip,zulip/zulip,rishig/zulip,shubhamdhama/zulip,rht/zulip,zulip/zulip,dhcrzf/zulip,brainwane/zulip,andersk/zulip,eeshangarg/zulip,tommyip/zulip,timabbott/zulip,andersk/zulip,kou/zulip,shubhamdhama/zulip,hackerkid/zulip,zulip/zulip,hackerkid/zulip,timabbott/zulip,timabbott/zulip,showell/zulip,eeshangarg/zulip,synicalsyntax/zulip,brainwane/zulip,eeshangarg/zulip,shubhamdhama/zulip,rishig/zulip,showell/zulip,kou/zulip,tommyip/zulip,dhcrzf/zulip,punchagan/zulip,hackerkid/zulip,timabbott/zulip