widgets: algin rect outline radius with inner border radius

[PaideiaDilemma]

Closes #611

To verify that the the outline of a box matches with the inner border perfectly,
I used this:

input-field {
  monitor=
  size=25%, 5%
  inner_color=rgba(fff7ed20)
  outer_color=rgba(fff7ed20)
  position=0, -20
  rounding=15
  fade_on_empty = false
  valign=center
}

Because inner and outer color have the same alpha, one can easily spot if they overlap or not.

Previously if the rounding was to big, it used rounding 0.
Now it clamps it to the maximum.

Tested:

• rouding -1 for shape, image and input-field
• rouding -1 and border for shape, image and input-field
• rounding 0 for shape, image and input-field
• rounding 0 and border for shape, image and input-field

[PaideiaDilemma]

Wait i don't think this is actually what we want. cause we don't want inner to have different rounding. looks off. we just need to scale the rounding correctly. no need for outerRounding

[PaideiaDilemma]

This is what we want i think.
The inner radius of the border just needed to be scaled properly.

Actually the problem just occurred in edge cases, where the rounding approached minhalf and a thick border was used.

[PaideiaDilemma]

This is what we want i think.
The inner radius of the border just needed to be scaled properly. No need for outerRadius in the shader.

Actually the problem just occurred in edge cases, where the rounding approached minhalf and a thick border was used.