msComputeBounds produces incorrect results when first shape has zero lines

[mchapman87501]

When rendering vector layers, msClipPolygonRect may yield shapes containing lines which have zero points. When a zero-point line occurs as the first line in a shape, msComputeBounds does not correctly compute the bounds of the shape.

This problem may manifest as a partially-filled map region when using e.g. the AGG/PNG driver.

I'll try to attach a test script which demonstrates the problem using shp2img, and also a patch for mapprimitive.c.

[mchapman87501]

Test script, mapfile and data to demonstrate the problem using shp2img

[mchapman87501]

Patch for mapprimitive.c, showing one way to fix the problem.

[tbonfort]

Thanks mchapmann for reporting, sorry this bug slipped passed me, I fell onto it while looking for duplicates in resolving #3383

fixed in r10378, r10379, r10380 for 5.4, 5.6 and trunk

resolves #3383