Use additional samples to test for constant parts of an axial gradient
The method doAxialShFill does adaptive sampling of gradients. If the gradient color is found to be the same at two consecutive sampling locations then the gradient is concluded to be constant between the two locations.
Of course, this conclusion may be wrong; one instance of this happening is
This patch fixes rendering of the test file in issue 938 by doing one more sampling when a part of the gradient is suspected to be constant. Of course it is easily possible to create gradients also misrender with the additional sampling point. Should such gradients ever appear in actual non-synthetic documents the code can now easily handle yet more sample points.
Fixes: #938 (closed)