Performance of API findFirstZero in python dumper.py is poor

The findFirstZero API is presenting poor performance under GDB.

Implementation (which is generic) could be improved under GDB using:

def findFirstZero(self, p, maximum):
l = len(p.string())
if l > maximum:
return -1, maximum
return 0,l

Base on my test, this is equivalent and faster for small null terminated string.