Avoid partial functions

[srghma]

e.g. here

streaming-commons/Data/Streaming/Process.hs

Lines 85 to 97 in 64d1959

	instance InputSource ClosedStream where
	isStdStream = (\(Just h) -> hClose h >> return ClosedStream, Just CreatePipe)
	instance InputSource Inherited where
	isStdStream = (\Nothing -> return Inherited, Just Inherit)
	instance InputSource UseProvidedHandle where
	isStdStream = (\Nothing -> return UseProvidedHandle, Nothing)
	instance OutputSink ClosedStream where
	osStdStream = (\(Just h) -> hClose h >> return ClosedStream, Just CreatePipe)
	instance OutputSink Inherited where
	osStdStream = (\Nothing -> return Inherited, Just Inherit)
	instance OutputSink UseProvidedHandle where
	osStdStream = (\Nothing -> return UseProvidedHandle, Nothing)