Ppsl: Input_Instance lazy reading for php://input (fuel#2125)

We should use on demand lazy reading for php://input, otherwise in nested Requests with php 5.6+ we have redundant re-reading it, and have unnecessary memory consumption and potentially DDoS, depending on the settings of frontend server, typically nginx (client_max_body_size).

classes/input/instance.php

@@ -87,9 +87,6 @@ public function __construct(Request $new = null, Input_Instance $input = null)
 		// store the associated request
 		$this->request = $new;
 
-		// get php raw input
-		$this->raw_input = file_get_contents('php://input');
-
 		// was an input instance passed?
 		if ($input)
 		{
@@ -328,6 +325,12 @@ public function method($default = 'GET')
 	 */
 	public function raw()
 	{
+		if ($this->raw_input === null)
+		{
+			// get php raw input
+			$this->raw_input = file_get_contents('php://input');
+		}
+
 		return $this->raw_input;
 	}