bug#39484: 26.3; try-completion bug

[Wanrong Lin]

try-completion does not work as expected when completion-ignore-case is t.

Examples:

(let ((completion-ignore-case t))
       (try-completion "xy" '("XyzD" "XyzAbc"))
       )
==> "Xyz"

Expected. The return value has uppercase "X", since the return value 
should be the maximum substring among all the *candidates*.

(let ((completion-ignore-case t))
       (try-completion "xyz" '("XyzD" "XyzAbc"))
       )
==> "xyz"

*Unexpected*. Should be "Xyz".

Thanks for looking into this.

Wanrong