patch 8.1.2090: not clear why channel log file ends

Problem:    Not clear why channel log file ends.
Solution:   Add a "closing" line.
diff --git a/src/channel.c b/src/channel.c
index e42c957..0ac9718 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -141,7 +141,13 @@
     FILE   *file = NULL;
 
     if (log_fd != NULL)
+    {
+	if (*fname != NUL)
+	    ch_log(NULL, "closing, opening %s", fname);
+	else
+	    ch_log(NULL, "closing");
 	fclose(log_fd);
+    }
 
     if (*fname != NUL)
     {