TASImage::DrawCircle() fails with semi-transparent color

[linev]

Check duplicate issues.

• Checked for duplicates

Description

When trying to call TASImage::FillCircle with semi-transparent color,
it stuck in endless loop inside ctx_flood_fill() function of asimage.

Failure was recognized long time ago, because TImageDump has strange workaround for it.
But it was never analyzed and fixed correctly.

I also did not found exact report in the JIRA - only related ROOT-3675 which was fixed some time ago.

Reproducer

{
   TASImage img(800, 800);
   img.DrawCircle(400, 400, 200, "#7FFF0000", -1);
}

ROOT version

master

Installation method

Build from source

Operating system

OpenSUSE

Additional context

No response