Raise when nan bounds are passed to tiles

[samn]

Otherwise the coordinate could get unintentionally clamped to the globe's extremeties:

mercantile/mercantile/__init__.py

Lines 533 to 536 in fe3762d

	w = max(-180.0, w)
	s = max(-85.051129, s)
	e = min(180.0, e)
	n = min(85.051129, n)

>>> from math import nan
>>> max(nan, -180)
nan
>>> min(nan, 180)
nan
>>> max(-180, nan)
-180
>>> min(180, nan)
180