vty: Fix logically dead code in the description handling

The code most likely wanted to check the result of argv_concat.
To do this we need to dereference the dptr.

Logically dead code (DEADCODE)
dead_error_line: Execution cannot reach this statement "return 1;

Fixes: Coverity CID 1040675
diff --git a/src/vty/logging_vty.c b/src/vty/logging_vty.c
index a6d2f52..e17c7a8 100644
--- a/src/vty/logging_vty.c
+++ b/src/vty/logging_vty.c
@@ -315,7 +315,7 @@
 	if (*dptr)
 		talloc_free(*dptr);
 	*dptr = argv_concat(argv, argc, 0);
-	if (!dptr)
+	if (!*dptr)
 		return CMD_WARNING;
 
 	return CMD_SUCCESS;