Fix discarding in circle shader.

[CleverSource]

Describe the issue (if no issue has been made)

When the alpha of an entity with a circle renderer is set to 0, complete transparency never happens, as a result of an issue with discarding logic in the circle shader. It would be expected to have complete transparency when alpha is set to 0.

Proposed fix (Make sure you've read on how to contribute to Hazel)

Instead of discarding when circle is set to 0.0 it should be preferred to discard when o_Color.a is set to 0.0.

Miscellaneous Fix

Made all spaced-sections to tabs for consistency. Preferred coding style seems to be to use tabs and not spaces.