Add missing pointer validation check in mountinfo

[atcuno]

The following backtrace triggered in the latest run.

Sample: broken_mount_enumeration_ubuntu_22_04_x64

25-01-31 19:00:27 volatility3.cli DEBUG    Traceback (most recent call last):
  File "/home/ub/volatility3/volatility3/cli/__init__.py", line 512, in run
    renderer.render(grid)
  File "/home/ub/volatility3/volatility3/cli/text_renderer.py", line 232, in render
    grid.populate(visitor, outfd)
  File "/home/ub/volatility3/volatility3/framework/renderers/__init__.py", line 240, in populate
    for level, item in self._generator:
  File "/home/ub/volatility3/volatility3/framework/plugins/linux/mountinfo.py", line 205, in _generator
    mnt_info = self.get_mountinfo(mnt, task)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/plugins/linux/mountinfo.py", line 101, in get_mountinfo
    st_dev = f"{superblock.major}:{superblock.minor}"
                ^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/objects/__init__.py", line 454, in __getattr__
    return getattr(self.dereference(), attr)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/symbols/linux/extensions/__init__.py", line 955, in major
    return self.s_dev >> self.MINORBITS
           ^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/objects/__init__.py", line 962, in __getattr__
    member = template(context=self._context, object_info=object_info)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/objects/templates.py", line 96, in __call__
    return self.vol.object_class(
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/objects/__init__.py", line 168, in __new__
    value = cls._unmarshall(context, data_format, object_info)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/objects/__init__.py", line 202, in _unmarshall
    data = context.layers.read(
           ^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/interfaces/layers.py", line 635, in read
    return self[layer].read(offset, length, pad)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/layers/linear.py", line 45, in read
    for offset, _, mapped_offset, mapped_length, layer in self.mapping(
  File "/home/ub/volatility3/volatility3/framework/layers/intel.py", line 326, in mapping
    for offset, size, mapped_offset, mapped_size, map_layer in self._mapping(
  File "/home/ub/volatility3/volatility3/framework/layers/intel.py", line 382, in _mapping
    chunk_offset, page_size, layer_name = self._translate(offset)
                                          ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ub/volatility3/volatility3/framework/layers/intel.py", line 166, in _translate
    raise exceptions.PagedInvalidAddressException(
volatility3.framework.exceptions.PagedInvalidAddressException: Page Fault at entry 0xcccccccccccccccc in page entry```

[gcmoreira]

it looks good