Fix logic error in _write_to_mem_with_gadget()

[astewart-bah]

raise RopException in _write_to_mem_with_gadget() when selected gadget does not pass the checks stating that the next pc must come from the stack rather than return False

_write_to_mem_with_gadget is called by _try_write_to_mem using the chain += syntax

_try_write_to_mem is called in a try except block for each gadget in _write_to_mem.

The except block excepts the following exceptions: RopException, angr.errors.SimEngineError, angr.errors.SimUnsatError

Before this change, if the first gadget checked with this workflow did not pass the check, the try block would fail to perform chain + False on this line:

angrop/angrop/rop_chain.py

Line 33 in 5d44d31

o_state = other._blank_state

with:

AttributeError: 'bool' object has no attribute '_blank_state'

Since AttributeErrors are not in the list of excepted errors, the next gadget is not tried.

Replacing the return False with raise RopException fixes this issue and allows all of the gadgets to be tried until a working mem writer chain is found.

[Kyle-Kyle]

thank you for the contribution!