[flang] Only deallocate intent(out) allocatable through runtime if allocated

Deallocation of intent(out) allocatable was done in D133348. This patch adds
an if guard when the deallocation is done through a runtime call. The runtime
is crashing if the box is not allocated. Call the runtime only if the box is
allocated. This is the case for derived type, polymorphic and unlimited
polymorphic entities.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D141427