Undefined behaviour in ptarray_segmentize2d

[Algunenano]

It comes from test test_lwgeom_segmentize2d:

	linein = lwgeom_from_wkt("LINESTRING(0 0,10 0)", LW_PARSER_CHECK_NONE);
	lwgeom_request_interrupt();
	lineout = lwgeom_segmentize2d(linein, 1e-100);
	CU_ASSERT_EQUAL(lineout, NULL);
	lwgeom_free(linein);

$ ./cunit/.libs/lt-cu_tester test_lwgeom_segmentize2d

Running test 'test_lwgeom_segmentize2d' in suite 'measures'.
ptarray.c:450:10: runtime error: 1e+101 is outside the range of representable values of type 'unsigned int'

I'll need to check if it affects both 3.0 and 2.5.

I feel that the code is probably filled with these kind of issues (unsafe casting from double to integer types), but since those are corner cases I'll limit myself to fix whatever comes up when running unit tests.

WIP in ​https://github.com/postgis/postgis/pull/292

[algunenano]

In 16723:

Fix undefined behaviour in ptarray_segmentize2d

Closes #4173
References #4153
Closes ​https://github.com/postgis/postgis/pull/292

[pramsey]

In 16922:

Get a little hard-core on NaN representation, hopefully won't break obscure architectures (more than they are already broken)
References #4173