[1.2.X] Fixed #15378 -- Now properly handle OGR layers that have features with...

[1.2.X] Fixed #15378 -- Now properly handle OGR layers that have features with invalid geometries.  Thanks, kunitoki for bug report and initial patch.

Backport of r15813 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15814 bcc190cf-cafb-0310-a4f2-bffc1f526a37