patch 9.0.1705: cursor position wrong when clicking on an unprintable char

Problem:  cursor position wrong when clicking on an unprintable char
Solution: Don't update prev_ptr when wlv.n_extra is not zero.

closes: #12664

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index 1754fb8..c4d6ef6 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -4036,4 +4036,47 @@
   bw!
 endfunc
 
+" Test clicking on a TAB or an unprintable character in Normal mode
+func Test_normal_click_on_ctrl_char()
+  let save_mouse = &mouse
+  set mouse=a
+  new
+
+  call setline(1, "a\<Tab>b\<C-K>c")
+  redraw
+  call test_setmouse(1, 1)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 1, 0, 1], getcurpos())
+  call test_setmouse(1, 2)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 2, 0, 8], getcurpos())
+  call test_setmouse(1, 3)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 2, 0, 8], getcurpos())
+  call test_setmouse(1, 7)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 2, 0, 8], getcurpos())
+  call test_setmouse(1, 8)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 2, 0, 8], getcurpos())
+  call test_setmouse(1, 9)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 3, 0, 9], getcurpos())
+  call test_setmouse(1, 10)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 4, 0, 10], getcurpos())
+  call test_setmouse(1, 11)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 4, 0, 10], getcurpos())
+  call test_setmouse(1, 12)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 5, 0, 12], getcurpos())
+  call test_setmouse(1, 13)
+  call feedkeys("\<LeftMouse>", 'xt')
+  call assert_equal([0, 1, 5, 0, v:maxcol], getcurpos())
+
+  bwipe!
+  let &mouse = save_mouse
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab