vim-patch:8.1.0963: illegal memory access when using 'incsearch'

Problem:    Illegal memory access when using 'incsearch'.
Solution:   Reset highlight_match when changing text. (closes vim/vim#4022)
4a7d2d3b40

src/nvim/misc1.c

@@ -1819,6 +1819,9 @@ void changed(void)
     changed_int();
   }
   buf_inc_changedtick(curbuf);
+
+  // If a pattern is highlighted, the position may now be invalid.
+  highlight_match = false;
 }
 
 /*