Fixing 0 length issue with constructor

[michaelgsharp]

Fixes #106538 by modifying the check in the constructor to also throw an error if the base memory length is 0.

[rameel]

This expression can be simplified...

if ((maxElements >= span.Length && span.Length != 0) || (span.Length == 0 && maxElements > 0))
    ThrowHelper.ThrowArgument_InvalidStridesAndLengths();

... to:

if (maxElements > 0 && maxElements >= span.Length)
    ThrowHelper.ThrowArgument_InvalidStridesAndLengths();

Explanation:

For simplicity, let's represent maxElements as a and span.Length as b. Now, the condition looks like this:

if ((a >= b && b != 0) || (b == 0 && a > 0))
    error;

We can normalize the condition by switching the order of the expressions (b == 0 && a > 0), resulting in:

if ((a >= b && b != 0) || (a > 0 && b == 0))
    error;

This can be interpreted as:

if ((a >= b && b != 0)  // a > 0, b > 0, a >= b
 || (a > 0  && b == 0)) // a > 0, b = 0
    error;

Thus, we are only interested in cases where a > 0, which simplifies the second part of the expression.

In the end, we get:

if (a > 0 && a >= b)
    error;

The final expression will look like this:

if (maxElements > 0 && maxElements >= span.Length)
    ThrowHelper.ThrowArgument_InvalidStridesAndLengths();

[michaelgsharp]

/backport to release/9.0

[github-actions]

Started backporting to release/9.0: https://github.com/dotnet/runtime/actions/runs/10889241013