We currently always crash if a user attempts to unmap a range that
does not intersect with an existing region, no matter the size. This
happens because we will never explicitly check to see if the search
for intersecting regions found anything, instead loop over the results,
which might be an empty vector. We then attempt to deallocate the
requested range from the `RangeAllocator` unconditionally, which will
be invalid if the specified range is not managed by the RangeAllocator.
We will assert validating m_total_range.contains(..) the range we are
requesting to deallocate.
This fix to this is straight forward, error out if we weren't able to
find any intersections.
You can get stress-ng to attempt this pattern with the following
arguments, which will attempt to unmap 0x0 through some large offset:
```
stress-ng --vm-segv 1
```
Fixes: #8483
Co-authored-by: Federico Guerinoni <guerinoni.federico@gmail.com>
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