patch 9.0.0198: ml_get error when switching buffer in Visual mode

Problem:    ml_get error when switching buffer in Visual mode.
Solution:   End Visual mode when switching buffer. (closes #10902)

src/testdir/test_visual.vim

@@ -1481,5 +1481,25 @@ func Test_visual_area_adjusted_when_hiding()
   bwipe!
 endfunc
 
+func Test_switch_buffer_ends_visual_mode()
+  enew
+  call setline(1, 'foo')
+  set hidden
+  set virtualedit=all
+  let buf1 = bufnr()
+  enew
+  let buf2 = bufnr()
+  call setline(1, ['', '', '', ''])
+  call cursor(4, 5)
+  call feedkeys("\<C-V>3k4h", 'xt')
+  exe 'buffer' buf1
+  call assert_equal('n', mode())
+
+  set nohidden
+  set virtualedit=
+  bwipe!
+  exe 'bwipe!' buf2
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab