patch 8.0.0762: ml_get error with :psearch in buffer without a name

Problem:    ml_get error with :psearch in buffer without a name. (Dominique
            Pelle)
Solution:   Use the buffer number instead of the file name.  Check the cursor
            position.
diff --git a/src/Makefile b/src/Makefile
index dcb9203..e522c78 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2216,6 +2216,7 @@
 	test_perl \
 	test_plus_arg_edit \
 	test_popup \
+	test_preview \
 	test_profile \
 	test_put \
 	test_python2 \