Fix bug where empty files where created for content plugins that did not render anything. (render callback returned null instead of a readStream)
Fix bug where empty files where created for content plugins that did not render anything. (render callback returned null instead of a readStream)

pridemusvaire/wintersmith,mimiflynn/wintersmith,MorJar/wintersmith,pridemusvaire/wintersmith,jmptrader/wintersmith,cwhatley/wintersmith,jnordberg/wintersmith,MorJar/wintersmith,1upon0/wintersmith,jmptrader/wintersmith,mimiflynn/wintersmith,taras/embersmith