Fix W1063 warning in IsBlankText by using WideChar($A0)

[ewsajjang]

This PR fixes the W1063 warning ("Widening given AnsiChar constant to WideChar lost information") in the IsBlankText function. Replace #160 with WideChar($A0) in IsBlankText to avoid W1063 warning.

Compiled and tested with D12, no warning observed.

[carloBarazzetta]

I don't have this warning: what version of Delphi 12 are you compiling with?

[ewsajjang]

Hello, @carloBarazzetta
Oh, I’m new to PRs and only recently learned that it’s good to discuss things first before submitting one. I’m compiling with Delphi 12.3 Athens in a Korean Windows environment. I think the W1063 warning is appearing because of the Korean locale (CP949), and it might be the same in other locales as well.