Fix "minimum" fan curve

[Smeat]

Hello,

first of all: Thank you very much for this program!

This PR fixes one small issue with the "minimum" fan curve.
By not setting a default value for min, it defaults to 0. This causes the math.Min function to always return 0 and thus rendering the "minimum" curve useless.
Setting it to 255 fixes this issue.

[markusressel]

Good catch!
Actually there is a test for the Minimum function, but it happens to exactly line up with this edge case: expecting 0 😆
See here:

fan2go/internal/curves/curve_test.go

Line 267 in 16f134f

func TestFunctionCurveMinimum(t *testing.T) {

Could you adjust this by changing temp1 to something higher than 40000, and then expect the appropriate (non-zero) value at the end? Thx!

[Smeat]

I totally missed the tests, sorry.

[markusressel]

No worries, I didn't check everything in the first place 😄
Thx!