MM-54260: In Browse Channel Modal fix member count on private channels and when there is only 1 member in the channel (#24452)

server/channels/store/sqlstore/channel_store.go

@@ -2312,6 +2312,10 @@ func (s SqlChannelStore) GetChannelsMemberCount(channelIDs []string) (_ map[stri
 	defer rows.Close()
 
 	memberCounts := make(map[string]int64)
+	// Initialize member counts for channels with zero members
+	for _, channelID := range channelIDs {
+		memberCounts[channelID] = 0
+	}
 	for rows.Next() {
 		var channelID string
 		var count int64

webapp/channels/src/components/browse_channels/browse_channels.tsx

@@ -116,6 +116,7 @@ export default class BrowseChannels extends React.PureComponent<Props, State> {
                 return result.data ? result.data.map((channel) => channel.id) : [];
             },
             );
+            this.props.privateChannels.forEach((channel) => channelIDsForMemberCount.push(channel.id));
             if (channelIDsForMemberCount.length > 0) {
                 this.props.actions.getChannelsMemberCount(channelIDsForMemberCount);
             }