patch 8.2.1046: insufficient tests for src/buffer.c

Problem:    Insufficient tests for src/buffer.c.
Solution:   Add more tests.  Move comments related tests to a separate file.
            (Yegappan Lakshmanan, closes #6325)
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 3d14358..fff4fdf 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -90,6 +90,7 @@
 	test_close_count \
 	test_cmdline \
 	test_command_count \
+	test_comments \
 	test_comparators \
 	test_compiler \
 	test_conceal \
@@ -341,6 +342,7 @@
 	test_close_count.res \
 	test_cmdline.res \
 	test_command_count.res \
+	test_comments.res \
 	test_comparators.res \
 	test_conceal.res \
 	test_const.res \