EmailNotification: address Use of uninitialized value in numeric eq (==)

Dependencies

• [2] 5WNGKHLZ Plugins: Add isEnabled method
• [3] QDJRQIFF If multiple dependent builds fail, send a single email
• [*] 5EQYVRWE Add a plugin mechanism

Change contents

• replacement in src/lib/Hydra/Plugin/EmailNotification.pm at line 15
  [2.320]→[2.320:375](∅→∅)
  − return $self->{config}->{email_notification} == 1;
  [2.320]

  [2.375]
  + return defined($self->{config}->{email_notification}) && $self->{config}->{email_notification} == 1;