run-webkit-tests: fix crash when trying to read a log that did not exist.

Tools/Scripts/webkitpy/layout_tests/servers/server_base.py

 # Copyright (C) 2011 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 192 matching lines @@
                 if stderr_text:
                     _log.error('%s stderr:' % self._name)
                     for line in stderr_text.splitlines():
                         _log.error('  %s' % line)
                 else:
                     _log.error('%s no stderr' % self._name)
             else:
                 _log.error('%s no stderr handle' % self._name)
         else:
             _log.error('%s no process' % self._name)
-        if self._error_log_path:
+        if self._error_log_path and self._filesystem.exists(self._error_log_path):
             error_log_text = self._filesystem.read_text_file(self._error_log_path)
             if error_log_text:
                 _log.error('%s error log (%s) contents:' % (self._name, self._error_log_path))
                 for line in error_log_text.splitlines():
                     _log.error('  %s' % line)
             else:
                 _log.error('%s error log empty' % self._name)
             _log.error('')
         else:
             _log.error('%s no error log' % self._name)
@@ skipping 44 matching lines @@
             except IOError, e:
                 if e.errno in (errno.EALREADY, errno.EADDRINUSE):
                     raise ServerError('Port %d is already in use.' % port)
                 elif self._platform.is_win() and e.errno in (errno.WSAEACCES,):  # pylint: disable=E1101
                     raise ServerError('Port %d is already in use.' % port)
                 else:
                     raise
             finally:
                 s.close()
         _log.debug('all ports are available')