Fix bounds error in shapereader for null records

[lgolston]

Rationale

As identified in issue #2087, FionaReader is currently throwing an error when iterating through the records,of the 10m Natural Earth rivers shapefile for North America, due to some entries that have attributes but no geometry. Since geometry is None in those cases, calling geometry.bounds fails. I checked and this is new to version 5.0.0 of the shapefile - the previous 4.1.0 version works without error.

Implications

The bug should be fixed.

[dopplershift]

Is the bounds property not used by our codebase at all? It would seem that while your patch fixes the initial problem, it would only delay failure until that property from the base Record class is accessed:

cartopy/lib/cartopy/io/shapereader.py

Lines 82 to 90 in 3ebd4a4

	@property
	def bounds(self):
	"""
	The bounds of this Record's :meth:`~Record.geometry`.
	"""
	if self._bounds is None:
	self._bounds = self.geometry.bounds
	return self._bounds

[lgolston]

That is an interesting question @dopplershift. I am not sure if it is used anywhere, but will look at editing the property definition you have highlighted since looking now it produces an error with both BasicReader and FionaReader on this dataset.

[lgolston]

The bounds property of class Record is now modified with the same check in case it is called.

I also looked at test_shapereader, and found it was only testing FionaReader (if fiona installed). The PR now modifies it to test both Readers, improving branch coverage for shapereader.

[dopplershift]

Thanks for the fix @lgolston !