Added getting the CellID in the constructor method.

[ADustyOldMuffin]

closes #690

This is my first contribution so I'm still getting used to the project so any constructive criticism is welcome!

All I did was instantiate a configuration in the LogOnDetails and AnonymousLogOnDetails constructors and grab the CellID and set it. Let me know if I should've set the default value elsewhere or if there's a better way to do this.

[yaakov-h]

Creating a new configuration and then immediately using it's values is fairly pointless, as it doesn't give the consumer of the library any chance to configure it.

Inside SteamUser, where we use the values from LogOnDetails and AnonymousLogOnDetails, we have access to the configuration object that the consumer has already configured through this.Client.Configuration.

A better approach would be where we use the values at this line:

logon.Body.cell_id = details.CellID;

to either check for the magic value zero and then use the configuration instead, or to make the value on the xxxDetails objects nullable and then perform a null-coalesce like so:

logon.Body.cell_id = details.CellID ?? Client.Configuration.CellID;

[codecov-io]

Codecov Report

Merging #722 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #722      +/-   ##
==========================================
+ Coverage   22.63%   22.69%   +0.05%     
==========================================
  Files          93       93              
  Lines        9568     9572       +4     
  Branches      795      795              
==========================================
+ Hits         2166     2172       +6     
+ Misses       7270     7268       -2     
  Partials      132      132

Impacted Files	Coverage Δ
...t2/SteamKit2/Steam/Handlers/SteamUser/SteamUser.cs	27.98% <100%> (+2.04%)	⬆️

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[ADustyOldMuffin]

I figured it was simpler than what I was doing to get the configuration, embarrassed I missed where to access it. Thanks for the help!

[yaakov-h]

Thanks!