Continue if configuration is missing

Rather than throwing an exception and outright failing, we'll just
return default values when expected configuration is missing. We may
make this more robust in the future.

Author: robmen

src/votive/WixPackageSettings.cs

@@ -223,9 +223,9 @@ public void Refresh()
             {
                 using (RegistryKey regKey = Registry.LocalMachine.OpenSubKey(this.rootPath, false))
                 {
-                    object regValue = regKey.GetValue(this.name, this.defaultValue, RegistryValueOptions.None);
+                    object regValue = regKey?.GetValue(this.name, this.defaultValue, RegistryValueOptions.None);
                     this.initialized = true;
-                    this.settingValue = (T) regValue;
+                    this.settingValue = regValue == null ? default(T) : (T)regValue;
                 }
             }