[3.12] gh-106524: Fix a crash in _sre.template() (GH-106525) (GH-106544)

[3.12] gh-106524: Fix a crash in _sre.template() (GH-106525) (GH-106544)

Some items remained uninitialized if _sre.template() was called with invalid
indices. Then attempt to clear them in the destructor led to dereferencing
of uninitialized pointer.
(cherry picked from commit 2ef1dc37f02b08536b677dd23ec51541a60effd7)

Co-authored-by: Radislav Chugunov <52372310+chgnrdv@users.noreply.github.com>