Fix $kAlphaStr in PHP libavifinfo implementation

PHP strings do not behave exactly like C string literals.
Fix for https://github.com/WordPress/wordpress-develop/pull/4612

Add more test cases in avifinfo_test.php.

Change-Id: I00194cb141a860ac5547cc2238907e591cc24156

avifinfo.php

diff --git a/avifinfo.php b/avifinfo.php
index 84a2e93..f4e9429 100644
--- a/avifinfo.php
+++ b/avifinfo.php
@@ -444,7 +444,7 @@
       } else if ( $box->type == 'auxC' ) {
         // See AV1 Image File Format (AVIF) 4
         // at https://aomediacodec.github.io/av1-avif/#auxiliary-images
-        $kAlphaStr       = "urn:mpeg:mpegB:cicp:systems:auxiliary:alpha";
+        $kAlphaStr       = "urn:mpeg:mpegB:cicp:systems:auxiliary:alpha\0";
         $kAlphaStrLength = 44; // Includes terminating character.
         if ( $box->content_size >= $kAlphaStrLength ) {
           if ( !( $data = read( $this->handle, $kAlphaStrLength ) ) ) {

tests/avifinfo_test.php

diff --git a/tests/avifinfo_test.php b/tests/avifinfo_test.php
index 4b03f9c..cbdf49e 100644
--- a/tests/avifinfo_test.php
+++ b/tests/avifinfo_test.php
@@ -15,21 +15,31 @@
 
 require_once('../avifinfo.php');
 
-$features = array( 'width'        => false, 'height'       => false,
-                   'bit_depth'    => false, 'num_channels' => false );
-$handle = fopen( 'avifinfo_test_1x1.avif', 'rb' );
-if ( $handle ) {
-  $parser  = new Avifinfo\Parser( $handle );
-  $success = $parser->parse_ftyp() && $parser->parse_file();
-  fclose( $handle );
-  if ( $success ) {
-    $features = $parser->features->primary_item_features;
+function test_avifinfo_parser( $file_name, $expected_width, $expected_height,
+                               $expected_bit_depth, $expected_num_channels ) {
+  $features = array( 'width'        => false, 'height'       => false,
+                     'bit_depth'    => false, 'num_channels' => false );
+  $handle = fopen( $file_name, 'rb' );
+  if ( $handle ) {
+    $parser  = new Avifinfo\Parser( $handle );
+    $success = $parser->parse_ftyp() && $parser->parse_file();
+    fclose( $handle );
+    if ( $success ) {
+      $features = $parser->features->primary_item_features;
+    }
+  }
+
+  if ( $features['width'] != $expected_width ||
+       $features['height'] != $expected_height ||
+       $features['bit_depth'] != $expected_bit_depth ||
+       $features['num_channels'] != $expected_num_channels ) {
+    echo 'Failure: '.$file_name.PHP_EOL;
+  } else {
+    echo 'Success: '.$file_name.PHP_EOL;
   }
 }
 
-if ( !$features['width'] || !$features['height'] ||
-     !$features['bit_depth'] || !$features['num_channels'] ) {
-  echo 'Failure'.PHP_EOL;
-} else {
-  echo 'Success'.PHP_EOL;
-}
+test_avifinfo_parser('avifinfo_test_1x1.avif', 1, 1, 8, 3);
+test_avifinfo_parser('avifinfo_test_2x2_alpha.avif', 2, 2, 8, 4);
+test_avifinfo_parser('avifinfo_test_1x1_10b_nopixi_metasize64b_mdatsize0.avif',
+                     1, 1, 10, 3);