hydra-notify step-finished: Don't barf if the step has no log file

Dependencies

• [2] NTEDD7T4 Provide a plugin hook for when build steps finish
• [3] PXTSKX4G Add buildQueued plugin hook
• [4] IE2PRAQU hydra-queue-runner: Send build notifications

Change contents

• replacement in src/script/hydra-notify at line 64
  [2.4265]→[2.4265:4302](∅→∅)
  − my $stepNr = shift @ARGV or die;
  [2.4265]

  [2.4302]
  + die if scalar @ARGV < 2;

  + my $stepNr = shift @ARGV;
• replacement in src/script/hydra-notify at line 68
  [2.4411]→[2.4411:4449](∅→∅)
  − my $logPath = shift @ARGV or die;
  [2.4411]

  [2.4449]
  + my $logPath = shift @ARGV;

  + $logPath = undef if $logPath eq "";