Fix error handling for paths that don't exist in syn.get('/path/file') used to throw 500 error.
Fix error handling for paths that don't exist in syn.get('/path/file') used to throw 500 error.

larssono/synapsePythonClient,thomasyu888/synapsePythonClient,zimingd/synapsePythonClient,kkdang/synapsePythonClient