Account for change in <sfile> in Vim 8.2

The output of expand('<sfile>') inside a function now differs in that it
lists multiple function names for nested calls delimited by '..'. We
need to extract the last function name to determine the current script
number.

Author: noahfrederick

autoload/composer.vim

@@ -57,7 +57,8 @@ endfunction
 ""
 " Get Funcref from script-local function {name}.
 function! s:function(name) abort
-  return function(substitute(a:name, '^s:', matchstr(expand('<sfile>'), '<SNR>\d\+_'), ''))
+  let func_name = split(expand('<sfile>'), '\.\.')[-1]
+  return function(substitute(a:name, '^s:', matchstr(func_name, '<SNR>\d\+_'), ''))
 endfunction
 
 ""