patch 8.0.0271: may get ml_get error when :tcldo deletes lines

Problem:    May get ml_get error when :tcldo deletes lines or switches to
            another buffer. (Nikolai Pavlov, closes #1421)
Solution:   Check the buffer and line every time.
diff --git a/src/Makefile b/src/Makefile
index f26a1bf..922a09b 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2198,6 +2198,7 @@
 	test_tabpage \
 	test_tagcase \
 	test_tagjump \
+	test_tcl \
 	test_textobjects \
 	test_timers \
 	test_true_false \