[Issue 20263] Wrong value for CustomFloat.min_exp

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20263

--- Comment #1 from Berni <dlang at croco-puzzle.com> ---
Sorry, should be 1, because 2^(1-1)=2^0=1 is minimum value.

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