patch 8.0.0331: restoring help snapshot accesses freed memory

Problem:    Restoring help snapshot accesses freed memory. (Dominique Pelle)
Solution:   Don't restore a snapshot when the window closes.
diff --git a/src/Makefile b/src/Makefile
index e1443e5..153e526 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2132,6 +2132,7 @@
 	test_goto \
 	test_gui \
 	test_hardcopy \
+	test_help \
 	test_help_tagjump \
 	test_hide \
 	test_history \