cleanup and logging

app/coffee/OutputFileOptimiser.coffee

@@ -6,6 +6,8 @@ logger = require "logger-sharelatex"
 module.exports = OutputFileOptimiser =
 
 	optimiseFile: (src, dst, callback = (error) ->) ->
+		# check output file (src) and see if we can optimise it, storing
+		# the result in the build directory (dst)
 		if src.match(/\.pdf$/)
 			OutputFileOptimiser.optimisePDF src, dst, callback
 		else
@@ -19,12 +21,13 @@ module.exports = OutputFileOptimiser =
 		proc = spawn("qpdf", args)
 		stdout = ""
 		proc.stdout.on "data", (chunk) ->
-			stdout += chunk.toString()	
-		proc.on "error", callback	
+			stdout += chunk.toString()
+		proc.on "error", callback
 		proc.on "close", (code) ->
 			if code != 0
 				logger.warn {directory, code}, "qpdf returned error"
 				return callback null
 			fs.rename tmpOutput, dst, (err) ->
-				# could log an error here
-				callback null
+				if err?
+					logger.warn {tmpOutput, dst}, "failed to rename output of qpdf command"
+				callback err