Undefined behavior in two AWS benchmarks

[mchalupa]

The following two benchmarks use uninitialized variables with automatic storage which is undefined behavior:

aws_priority_queue_init_dynamic_harness-1.i uses initial_item_allocation without inicialization: https://github.com/sosy-lab/sv-benchmarks/blob/master/c/aws-c-common/aws_priority_queue_init_dynamic_harness-1.i#L7919

aws_byte_buf_write_from_whole_buffer_harness-1.i uses the structure buf without inicialization here: https://github.com/sosy-lab/sv-benchmarks/blob/master/c/aws-c-common/aws_byte_buf_write_from_whole_buffer_harness-1.i#L8987