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/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 58291ea..3ff7247 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -154,6 +154,7 @@
 	    test_gn.res \
 	    test_gui.res \
 	    test_hardcopy.res \
+	    test_help.res \
 	    test_hide.res \
 	    test_history.res \
 	    test_hlsearch.res \