patch 9.1.0446: getregionpos() inconsistent for partly-selected multibyte char

Problem:  getregionpos() behaves inconsistently for a partly-selected
          multibyte char.
Solution: Always use column of the first byte for a partly-selected
          multibyte char (zeertzjq).

closes: #14851

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_visual.vim b/src/testdir/test_visual.vim
index e1c7cf5..95ac9a6 100644
--- a/src/testdir/test_visual.vim
+++ b/src/testdir/test_visual.vim
@@ -2073,10 +2073,12 @@
           \ getregion(getpos('v'), getpos('.'), {'type': "\<C-v>" }))
     call assert_equal([
           \   [[bufnr('%'), 1, 5, 0], [bufnr('%'), 1, 5, 0]],
-          \   [[bufnr('%'), 2, 10, 1], [bufnr('%'), 2, 10, 2]],
+          \   [[bufnr('%'), 2, 7, 1], [bufnr('%'), 2, 7, 2]],
           \   [[bufnr('%'), 3, 5, 0], [bufnr('%'), 3, 5, 0]],
           \ ],
           \ getregionpos(getpos('v'), getpos('.'), {'type': "\<C-v>" }))
+    call assert_equal(['efghijk«', '🇦«ðŸ‡§«ðŸ‡¨«ðŸ‡©', '12345'],
+          \ getregion(getpos('v'), getpos('.'), {'type': 'v' }))
     call assert_equal([
           \   [[bufnr('%'), 1, 5, 0], [bufnr('%'), 1, 13, 0]],
           \   [[bufnr('%'), 2, 1, 0], [bufnr('%'), 2, 22, 0]],
@@ -2084,6 +2086,28 @@
           \ ],
           \ getregionpos(getpos('v'), getpos('.'), {'type': 'v' }))
 
+    call cursor(1, 5)
+    call feedkeys("\<Esc>\<C-v>5l2j", 'xt')
+    call assert_equal(['efghij', ' «ðŸ‡¨« ', '567890'],
+          \ getregion(getpos('v'), getpos('.'), {'type': "\<C-v>" }))
+    call assert_equal([
+          \   [[bufnr('%'), 1, 5, 0], [bufnr('%'), 1, 10, 0]],
+          \   [[bufnr('%'), 2, 7, 1], [bufnr('%'), 2, 19, 1]],
+          \   [[bufnr('%'), 3, 5, 0], [bufnr('%'), 3, 10, 0]],
+          \ ],
+          \ getregionpos(getpos('v'), getpos('.'), {'type': "\<C-v>" }))
+
+    call cursor(1, 4)
+    call feedkeys("\<Esc>\<C-v>02j", 'xt')
+    call assert_equal(['abcd', '🇦« ', '1234'],
+          \ getregion(getpos('v'), getpos('.'), {'type': "\<C-v>" }))
+    call assert_equal([
+          \   [[bufnr('%'), 1, 1, 0], [bufnr('%'), 1, 4, 0]],
+          \   [[bufnr('%'), 2, 1, 0], [bufnr('%'), 2, 7, 1]],
+          \   [[bufnr('%'), 3, 1, 0], [bufnr('%'), 3, 4, 0]],
+          \ ],
+          \ getregionpos(getpos('v'), getpos('.'), {'type': "\<C-v>" }))
+
     #" characterwise selection with multibyte chars
     call cursor(1, 1)
     call feedkeys("\<Esc>vj", 'xt')