ast: fix (*ast.File).End check shadow no entry

[visualfc]

fix (*ast.File).End bad result if classfile add shadow func Classfname.

example get.yap ast.File.End return last shadow func Classfname.End()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.27%. Comparing base (f3b7a43) to head (da59ab6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1860   +/-   ##
=======================================
  Coverage   93.27%   93.27%           
=======================================
  Files          40       40           
  Lines       11597    11597           
=======================================
  Hits        10817    10817           
  Misses        623      623           
  Partials      157      157           

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