Bill projection does not fail when less than 12 months of bill data available
Created by: adarsh-murthy
In bill.py, validate_raw_bill returns -1 for invalid bill. This is considered as True. Update the function to return -1, 0 and 1 where each number has its own case. -1 -> Bill is not present 0 -> Invalid bill, meaning less than 12 months of data is present 1 -> valid bill with at least 12 months of data