Describe the bug

When using GC#fillGradientRectangle with y < 0, color is not applied between y and 0.

By example, this causes a bug in the Eclipse Graphiti library, where you can create diagrams with elements with negative coordinates
https://gitlab.eclipse.org/eclipse/graphiti/graphiti

To Reproduce

In Eclipse SDK :

1. Help -> Install New Software
2. Select Graphiti Examples and install it
3. File -> New -> Other... -> Graphiti Example Diagram
4. Open the diagram created, and add EClass inside.
5. Move the EClass higher and scroll so that its y is < 0

Expected behavior

GC#fillGradientRectangle should also color with a y < 0, which is the case on Windows and Linux

Screenshots

In the above screenshot,

• the y of A is < 0 for its entire height
• the y of B is < 0 at the beginning then is > 0
• the y of C is > 0 for its entire height
  

Environment:

• • All OS
• • Windows
• • Linux
• • macOS

Additional context

This bug was introduced by commit 4f5f2dc