condense: Do not cache message_content height of 0 from recent_topics.
condense: Do not cache message_content height of 0 from recent_topics.

Previously, we suffered a bug where we would not properly condense
messages on first load of CZO (ie after login).

This bug was an unintended consequence of setting recent topics as the
default view, because since the page loads to recent_topics the
message_list is hidden but still gets rendered into the DOM and when
condense_and_collapse runs, it causes get_message_height to cache a
message height of 0, which results in the message not being collapsed.
There may be other ways to trigger the same broken mechanism.

This commit changes the function so we only return 0 but don't cache
the result.

Fixes: #20666.

eeshangarg/zulip,rht/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,andersk/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,zulip/zulip,kou/zulip,zulip/zulip,andersk/zulip,rht/zulip,kou/zulip,zulip/zulip,andersk/zulip,kou/zulip,andersk/zulip,kou/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip