patch 9.1.0056: wrong number of trailing spaces inserted after blockwise put

Problem:  Incorrect number of trailing spaces inserted for multibyte
	  characters when pasting a blockwise register in blockwise visual
          mode (VanaIgr)
Solution: Skip over trailing UTF-8 bytes when computing the number of trailing
          spaces (VanaIgr)

When pasting in blockwise visual mode, and the register type is <CTRL-V>, Vim
aligns the text after the replaced area by inserting spaces after pasted
lines that are shorter than the longest line. When a shorter line contains
multibyte characters, each trailing UTF-8 byte's width is counted in addition
to the width of the character itself. Each trailing byte counts as being 4
cells wide (since it would be displayed as <xx>).

closes: #13909

Signed-off-by: VanaIgr <vanaigranov@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: vanaigr

src/register.c

@@ -1903,10 +1903,10 @@ do_put(
 		spaces = y_width + 1;
 		init_chartabsize_arg(&cts, curwin, 0, 0,
 						      y_array[i], y_array[i]);
-		for (j = 0; j < yanklen; j++)
+
+		while (*cts.cts_ptr != NUL)
 		{
-		    spaces -= lbr_chartabsize(&cts);
-		    ++cts.cts_ptr;
+		    spaces -= lbr_chartabsize_adv(&cts);
 		    cts.cts_vcol = 0;
 		}
 		clear_chartabsize_arg(&cts);

src/testdir/test_put.vim

@@ -12,6 +12,16 @@ func Test_put_block()
   bwipe!
 endfunc
 
+func Test_put_block_unicode()
+  new
+  call setreg('a', "À\nÀÀ\naaaaaaaaaaaa", "\<C-V>")
+  call setline(1, [' 1', ' 2', ' 3'])
+  exe "norm! \<C-V>jj\"ap"
+  let expected = ['À           1', 'ÀÀ          2', 'aaaaaaaaaaaa3']
+  call assert_equal(expected, getline(1, 3))
+  bw!
+endfunc
+
 func Test_put_char_block()
   new
   call setline(1, ['Line 1', 'Line 2'])

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    56,
 /**/
     55,
 /**/