fix malformed pptx issue (#761)
* fix malformed pptx issue
Added a new test to check for the ability to partition a malformed PowerPoint file. Modified the `partition_pptx` function to skip processing shapes that are not on the actual slide, but only if they have top and left positions. Also modified `_order_shapes` function to handle cases where shapes do not have top or left positions.
* update changelog
* fix lint issue SIM102 nested ifs
* fix black linting
