fixes cowboy#1 on cowboy/php-simple-proxy

Change all UNDEFINED notices to not trigger (use array_key_exists instead)

ba-simple-proxy.php

@@ -163,8 +163,8 @@
     curl_setopt( $ch, CURLOPT_POST, true );
     curl_setopt( $ch, CURLOPT_POSTFIELDS, $_POST );
   }
-  
-  if ( $_GET['send_cookies'] ) {
+
+  if ( array_key_exists('send_cookies', $_GET) ) {
     $cookie = array();
     foreach ( $_COOKIE as $key => $value ) {
       $cookie[] = $key . '=' . $value;
@@ -180,9 +180,9 @@
   curl_setopt( $ch, CURLOPT_FOLLOWLOCATION, true );
   curl_setopt( $ch, CURLOPT_HEADER, true );
   curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
-  
-  curl_setopt( $ch, CURLOPT_USERAGENT, $_GET['user_agent'] ? $_GET['user_agent'] : $_SERVER['HTTP_USER_AGENT'] );
-  
+
+  curl_setopt( $ch, CURLOPT_USERAGENT, array_key_exists('user_agent', $_GET) ? $_GET['user_agent'] : $_SERVER['HTTP_USER_AGENT'] );
+
   list( $header, $contents ) = preg_split( '/([\r\n][\r\n])\\1/', curl_exec( $ch ), 2 );
 
   $status = curl_getinfo( $ch );
@@ -193,7 +193,7 @@
 // Split header text into an array.
 $header_text = preg_split( '/[\r\n]+/', $header );
 
-if ( $_GET['mode'] == 'native' ) {
+if ( array_key_exists('mode', $_GET) && $_GET['mode'] == 'native' ) {
   if ( !$enable_native ) {
     $contents = 'ERROR: invalid mode';
     $status = array( 'http_code' => 'ERROR' );
@@ -214,7 +214,7 @@
   $data = array();
 
   // Propagate all HTTP headers into the JSON data object.
-  if ( $_GET['full_headers'] ) {
+  if ( array_key_exists('full_headers', $_GET) ) {
     $data['headers'] = array();
 
     foreach ( $header_text as $header ) {
@@ -226,7 +226,7 @@
   }
 
   // Propagate all cURL request / response info to the JSON data object.
-  if ( $_GET['full_status'] ) {
+  if ( array_key_exists('full_status', $_GET) ) {
     $data['status'] = $status;
   } else {
     $data['status'] = array();