view: avoid "1+ messages" in per-message footer of /t/ and /T/

Try to appear gramatically correct and state:
"only message in thread" when there's only one known (to us)
message in the thread.

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index 62bdf0a1..47a2046e 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -458,7 +458,8 @@ sub thread_html {
         $ctx->{prev_level} = 0;
         $ctx->{root_anchor} = anchor_for($mid);
         $ctx->{mapping} = {};
-        $ctx->{s_nr} = "$nr+ messages in thread";
+        $ctx->{s_nr} = ($nr > 1 ? "$nr+ messages" : 'only message')
+                       .' in thread';
 
         my $rootset = thread_results($ctx, $msgs);