patch 8.2.0019: cannot number of lines of another buffer

Problem:    Cannot number of lines of another buffer.
Solution:   Add "linecount" to getbufinfo(). (Yasuhiro Matsumoto,
            closes #5370)
diff --git a/src/testdir/test_bufwintabinfo.vim b/src/testdir/test_bufwintabinfo.vim
index bebaca6..d61670b 100644
--- a/src/testdir/test_bufwintabinfo.vim
+++ b/src/testdir/test_bufwintabinfo.vim
@@ -154,3 +154,13 @@
   call assert_equal(getbufinfo('Xtestfile2')[0].lastused, 7654321)
   call test_settime(0)
 endfunc
+
+func Test_getbufinfo_lines()
+  new Xfoo
+  call setline(1, ['a', 'bc', 'd'])
+  let bn = bufnr('%')
+  hide
+  call assert_equal(3, getbufinfo(bn)[0]["linecount"])
+  edit Xfoo
+  bw!
+endfunc