fix(errors) Show previous error in trace

This helps knowing exactly where the first error happenened.

issue #6071

include/errors/class_FatalError.inc

@@ -84,10 +84,6 @@ class FatalError extends Error
       $config->get_cfg_value('displayerrors') == 'TRUE') {
       $trace    = FusionDirectoryError::formatTrace($this);
       $display  .= print_a($trace, TRUE);
-      $previous = $this;
-      while ($previous = $previous->getPrevious()) {
-        $display .= print_a(FusionDirectoryError::formatTrace($previous), TRUE);
-      }
     }
 
     $display .= '</body></html>';

include/errors/class_FusionDirectoryError.inc

@@ -76,6 +76,10 @@ class FusionDirectoryError extends Error
       ]
     );
 
+    if ($previous = $throwable->getPrevious()) {
+      $trace[] = static::formatTrace($previous);
+    }
+
     return $trace;
   }
 }