fix: improve FeedExpander (#3103)

* fix: improve FeedExpander

Include the first libxml error in exception.

Give better error message if trying to parse the empty string.

Log all libxml errors if debug mode is enabled.

* error handling and logging tweak

lib/RssBridge.php

@@ -41,7 +41,25 @@ final class RssBridge
             // Drop the current frame
             Logger::warning($text);
             if (Debug::isEnabled()) {
-                print sprintf('<pre>%s</pre>', $text);
+                print sprintf("<pre>%s</pre>\n", e($text));
+            }
+        });
+
+        // There might be some fatal errors which are not caught by set_error_handler() or \Throwable.
+        register_shutdown_function(function () {
+            $error = error_get_last();
+            if ($error) {
+                $message = sprintf(
+                    'Fatal Error %s: %s in %s line %s',
+                    $error['type'],
+                    $error['message'],
+                    trim_path_prefix($error['file']),
+                    $error['line']
+                );
+                Logger::error($message);
+                if (Debug::isEnabled()) {
+                    print sprintf("<pre>%s</pre>\n", e($message));
+                }
             }
         });