GradientFill does not draw properly

Steps to reproduce:

• Download and run Area_upper_bound_29.exe
• Switch the test to "Gradient Fill"
• Result: draws incorrectly then crashes the system (BSOD tracked in CORE-19634)

Behavior is the same in 0.4.8-dev-112-g7532c41 and 0.4.16-dev-1504-g206b528. Windows 10 screenshot attached for comparison.

Full-Sized Display from W2K3 of Area - Gradient Fill

Old description:

Fill triangle with one solid color works. Multi-color goes into a loop at dy is 0.

(../../win32ss/gdi/eng/gradient.c:363) FIXME: IntEngGradientFillTriangle is broken

(../../win32ss/gdi/eng/gradient.c:373) IntEngGradientFillTriangle loop 1 Count 1

(../../win32ss/gdi/eng/gradient.c:377) IntEngGradientFillTriangle in loop 1 EnumMore 0

(../../win32ss/gdi/eng/gradient.c:391) IntEngGradientFillTriangle in loop 1a y 299 sy 344 bt 374

(../../win32ss/gdi/eng/gradient.c:396) DOLINE 1

(../../win32ss/gdi/eng/gradient.c:396) DOLINE 2

(../../win32ss/gdi/eng/gradient.c:396) DOLINE 3

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 240 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 210 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 180 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 150 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 120 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 90 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 60 dy 30

(../../win32ss/gdi/eng/gradient.c:396) STEPCOL ec 30 dy 30

(../../win32ss/gdi/eng/gradient.c:396) DOLINE 4

(../../win32ss/gdi/eng/gradient.c:398) IntEngGradientFillTriangle in loop 1a 1

(../../win32ss/gdi/eng/gradient.c:400) IntEngGradientFillTriangle in loop 1a 1a

(../../win32ss/gdi/eng/gradient.c:401) DOLINE 1

(../../win32ss/gdi/eng/gradient.c:401) STEPCOL ec 255 dy 0

(../../win32ss/gdi/eng/gradient.c:401) STEPCOL ec 255 dy 0

(../../win32ss/gdi/eng/gradient.c:401) STEPCOL ec 255 dy 0