Pattern hatches with a predefined pattern (ANSI31, …) render as a solid fill

[cstaerkel]

Problem

EntityRenderDispatcher.DrawHatch decides that a hatch is a solid fill with

if (hatch.IsSolid || hatch.PatternType == HatchPatternType.SolidFill)

Hatch.PatternType is DXF group 76. The DXF reference defines that group as hatch pattern type:
0 = user-defined, 1 = predefined, 2 = custom. ACadSharp's enum names the value 1 SolidFill
(HatchPatternType.SolidFill = 1), but that is only a name: a hatch read from a DWG or DXF with a stock
pattern such as ANSI31 carries group 76 = 1 and group 70 (IsSolid) = 0. Whether a hatch is a solid fill is
group 70 alone.

The second half of the condition therefore catches every predefined-pattern hatch read from a file, which is
the most common kind, and fills it solid. The pattern path below it (ExplodePattern, MaxHatchLines) is
correct but is only reached by hatches built in code with PatternType = PatternFill, which is why the existing
tests pass.

Fix

if (hatch.IsSolid)

A solid hatch always has IsSolid set; the library's own SquareHatch(solid: true) and SyntheticSamples set
both, so nothing that is solid today stops being solid.

Test

PredefinedPatternHatchDrawsItsPatternRatherThanAFill builds the existing pattern hatch fixture with
PatternType = SolidFill and IsSolid = false, as a file reader produces it, and asserts lines are drawn and
no fill. It fails before the change (FillPath is called) and passes after.