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/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 36279d8..1f8d307 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -175,6 +175,7 @@
 	    test_packadd.res \
 	    test_paste.res \
 	    test_perl.res \
+	    test_preview.res \
 	    test_profile.res \
 	    test_python2.res \
 	    test_python3.res \