patch 8.2.0435: channel contents might be freed twice

Problem:    Channel contents might be freed twice.
Solution:   Call either channel_free_channel() or channel_free(), not both.
            (Nobuhiro Takasaki, closes #5835)
diff --git a/src/channel.c b/src/channel.c
index d5240fc..6dde107 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -4457,9 +4457,11 @@
 	    if (channel->ch_killing)
 	    {
 		channel_free_contents(channel);
+		channel_free_channel(channel);
 		channel->ch_job->jv_channel = NULL;
 	    }
-	    channel_free(channel);
+	    else
+		channel_free(channel);
 	    // channel has been freed, start over
 	    channel = first_channel;
 	    continue;