Fix IllegalArgumentException in Colors view

Fix IllegalArgumentException in Colors view

The return value of ColorDialog.getRGB can return null.

Bug: 408074
Change-Id: I40277621ba3e63b610e1ad2e012263850c74f26e
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/12856
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
IP-Clean: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
IP-Clean: Patrick Tasse <patrick.tasse@gmail.com>