vim-patch:8.0.0250

Problem:    When virtcol() gets a column that is not the first byte of a
            multi-byte character the result is unpredictable. (Christian
            Ludwig)
Solution:   Correct the column to the first byte of a multi-byte character.
            Change the utf-8 test to new style.

0c0590d982

Closes #6269

src/nvim/charset.c

@@ -1166,6 +1166,7 @@ void getvcol(win_T *wp, pos_T *pos, colnr_T *start, colnr_T *cursor,
       pos->col = 0;
     }
     posptr = ptr + pos->col;
+    posptr -= utf_head_off(line, posptr);
   }
 
   // This function is used very often, do some speed optimizations.