N°2013 Setup : fix crash on setting readonly mode if initial DB info were wrong

Same as 15d3201a, but this error happened before compilation, when setting read only mode.
As before this is another fix for #351.

This fix introduces the new method \WizardController::GetParamForConfigArray
I replaced existing duplicate code with a call to this new generic method.

core/config.class.inc.php

@@ -2469,11 +2469,14 @@ class Config
 	/**
 	 * Helper function to initialize a configuration from the page arguments
 	 *
+	 * @see \Parameters::GetParamForConfigArray() to get aParamValues from {@see Parameters} object hierarchy in setup
+	 * @see \WizardController::GetParamForConfigArray() to get aParamValues from {@see \WizardController} object hierarchy in setup
+	 *
 	 * @param array $aParamValues
-	 * @param string|null $sModulesDir
+	 * @param ?string $sModulesDir
 	 * @param bool $bPreserveModuleSettings
 	 *
-	 * @return void
+	 * @return void The current object is modified directly
 	 *
 	 * @throws \Exception
 	 * @throws \CoreException