Fix Socket array length to avoid possible out of bounds errors

[cheenamalhotra]

Following discussion from #1016..
This change fixes possible out of bounds errors and timeout cancellation issues.
Further improvements to be reviewed in #1029.

[Wraith2]

Is GetHostAddresses required to return a non-null value even if it can't resolve? If not you need to add a null check and probably early exit.

Also, while you're there... any chance of hoisting that AddressFamily array out as a static readonly so we can avoid allocating and discarding it every single time we make a connection?

[cheenamalhotra]

@Wraith2 regarding AddressFamily suggestion, there's another PR bringing in preferred family support: https://github.com/dotnet/SqlClient/pull/1015/files#diff-11cfbefb2cd1b54e3dfda7a8eeb5d1b447086f5dbb41204151929886c29ae99fR345 so it won't be a static.

I'll see improvement opportunity to reduce allocation with that PR.

[Wraith2]

Ok, LGTM then.