Return minimal QgsRectangle as boundingBox if geometry not available, since QgsRectangle(0,0,0,0) may be a valid bounding box for some geometries
Skip missing geometries when calculating extent (fixes #8192, #8194)
Merge pull request #789 from nyalldawson/bug8192

Fix bounding box calculation for features with NULL geometry (fixes #8192, #8194)