Fixing reading of multiple app context switches from a single AppContextSwitchOverrides configuration field.

[tetolv]

Description

SqlAppContextSwitchManager was unable to correctly parse multiple switches from the single configuration field. In case of such sample configuration:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section type="Microsoft.Data.SqlClient.AppContextSwitchOverridesSection, Microsoft.Data.SqlClient" name="AppContextSwitchOverrides"/>
  </configSections>
  <AppContextSwitchOverrides value="Switch.Microsoft.Data.SqlClient.EnableUserAgent=true;Switch.Microsoft.Data.SqlClient.UseCompatibilityProcessSni=true;System.Globalization.Invariant=false;"/>
</configuration>

following parsing code :

            string[] switches = appContextSwitches.Value?.Split('=', ';');
            ...
            for (int i = 0; i < switches.Length / 2; i++)
            {
                try
                {
                    AppContext.SetSwitch(switches[i], Convert.ToBoolean(switches[i + 1]));
                    SqlClientEventSource.Log.TryTraceEvent("<sc.{0}.{1}|INFO> Successfully assigned the AppContext switch '{2}'={3}.",
                                                           TypeName, methodName, switches[i], switches[i + 1]);
                }
                ...
            }

, on the second iteration would confuse switch key with a value and would try to convert key name to bool, which would of course fail.

One additional fix is for proper handling of configuration field, if it's content (sequence of switch=value pairs) starts, or ends with semicolon.

Testing

Changes seems trivial, bet unittests could be added, if deemed necessary.