[FfmpegAdapter] #running? incorrectly returns true when pidfile doesn't exist

[cjcolvar]

Passing nil to running? should return false but returns true because nil.to_i == 0

active_encode/lib/active_encode/engine_adapters/ffmpeg_adapter.rb

Lines 273 to 278 in f35a797

	def running?(pid)
	Process.getpgid pid.to_i
	true
	rescue Errno::ESRCH
	false
	end