move response.send() function before zipcode validation, add log statements

#### What's this PR do?
During the DonorsChoose.org donation flow, if a user inputs an invalid zipcode, our `isValidZip()` validator returns us out of the function **before** our `retrieveLocation()` function returns a response. MobileCommons is left hanging, and we're sent a timeout error. 

To minimize these errors, given that we're handling the user's incorrect input by opting them into a new reminder message, I've moved the response.send() higher before the validation flow. 

We've also added some log statements to let us know if a user doesn't submit a valid zipcode or state abbreviation.

#### How should this be manually tested?
This has been tested by correctly running through the donations flow, and also by inputting an incorrectly formatted zipcode. In each case, we were able to successfully run through the donations flow.