[1.5.x] Revert "Fixed #19895 -- Made second iteration over invalid queryset raise an exception too"

This reverts commit d1e87eb3baf75b1b6a0ada46a9b77f7e347cdb60.
This commit was the cause of a memory leak. See ticket for more details.
Thanks Anssi Kääriäinen for identifying the source of the bug.