Fix #11362: Use readfile instead of custom file_send_chunk

PHP's inbuilt readfile() function already does its own internal
chunking. We should use this function instead of our own file chunk
reading function to improve reliability and performance.

file_download.php

@@ -155,7 +155,7 @@
 				}
 
 				header( 'Content-Type: ' . $t_content_type );
-				file_send_chunk( $t_local_disk_file );
+				readfile( $t_local_disk_file );
 			}
 			break;
 		case FTP:
@@ -190,39 +190,3 @@
 			header( 'Content-Type: ' . $t_content_type );
 			echo $v_content;
 	}
-	exit();
-
-function file_send_chunk($filename, $start = 0, $maxlength = 0 ) {
-    static $s_safe_mode = null;
-    $chunksize = 4*131072;
-    $buffer = '';
-	$offset = $start;
-
-	if( $s_safe_mode == null ) {
-		$s_safe_mode = ini_get('safe_mode');
-	}
-
-    while (true) {
-		if ( $s_safe_mode == false) {
-			@set_time_limit(60*60); //reset time limit to 60 min - should be enough for 1 MB chunk
-		}
-        $buffer = file_get_contents($filename, 0, null, $offset, ( ($maxlength > 0 && $maxlength < $chunksize) ? $maxlength : $chunksize ) );
-        if ( $buffer === false ) {
-			if( $maxlength > 0 ) {
-				$buffer = file_get_contents($filename, 0, null, $offset, $maxlength );
-			} else {
-				$buffer = file_get_contents($filename, 0, null, $offset );			
-			}
-			echo $buffer;
-			flush();
-        	exit(); // end of file
-        }
-        echo $buffer;
-        flush();
-        $offset += $chunksize;
-        $maxlength -= $chunksize;
-        unset($buffer);
-        $buffer = null;
-    }
-    return;
-}