Optimized fuzz.py

[rahul-nath]

Simplified logic using De Morgan's Laws. Combined some lines to reduce string concatenation costs and make coding decisions more uniform. Hope they help.

[josegonzalez]

Sorry for not looking at this sooner. Is this a speed optimization, and if so, do you have benchmarks?

[maxbachmann]

@josegonzalez It's a line count optimisation. However in my opinion at least the string joining hurts readability.