vim-patch:8.1.1639: changing an autoload name into a file name is inefficient

Problem:    Changing an autoload name into a script file name is inefficient.
Solution:   Remember the last replaced #. (Ozaki Kiichi, closes vim/vim#4618)
28fc247f8d

src/nvim/eval.c

@@ -22025,6 +22025,7 @@ static bool script_autoload(const char *const name, const size_t name_len,
 }
 
 /// Return the autoload script name for a function or variable name
+/// Caller must make sure that "name" contains AUTOLOAD_CHAR.
 ///
 /// @param[in]  name  Variable/function name.
 /// @param[in]  name_len  Name length.