Throw IllegalArgumentException if invalid parameters are set

[Cliabhach]

The following situations should not be supported in v1:

• StarSize is not specified or equal to 0 and any of the following are true
  1. Empty drawable and filled drawable are different sizes
  2. Empty drawable and filled drawable are both size 0
  3. Empty drawable is not a square
  4. Filled drawable is not a square

N.B. arbitrary rectangles may be supported in a future release