zero rather than random extend during optimisation

Author: DRMacIver

hypothesis-python/src/hypothesis/internal/conjecture/optimiser.py

@@ -124,8 +124,10 @@ def attempt_replace(v):
  # component we want to give it a couple of tries to succeed.
  for _ in range(3):
  attempt = self.engine.cached_test_function(
- prefix + v_as_bytes + self.current_data.buffer[block.end :],
- extend=BUFFER_SIZE,
+ prefix
+ + v_as_bytes
+ + self.current_data.buffer[block.end :]
+ + bytes(BUFFER_SIZE),
  )
 
  if self.consider_new_test_data(attempt):