ValueError: math domain error if value == 0

[sgelb]

If termgraph is used as a module and a value is 0, a ValueError: math domain error is thrown by math.log in utils.py::cvt_to_readable(num) here:

termgraph/termgraph/utils.py

Line 16 in 09e17cc

index = int(math.log(num) / math.log(1000))

Problem is that there is there is no zero check for num. This is done correctly in termgraph.py::cvt_to_readable(num):

termgraph/termgraph/termgraph.py

Line 197 in 4aa3b67

if num != 0:

[frankbryce]

I made a pull request to fix this.