Fix index to list when there is no 2nd element

[noelevans]

When the module is run like this:
python top_pic_comments.py
the variable sys.argv is:
['top_pic_comments.py']
So only a 0th element is available, not a 1st. Simple fix to check the length of argv

Testing below:

Before fix

With numerical arg after module name

python top_pic_comments.py 1
Title of submission:
After floods in England, swans in the street - Worcester
http://i.imgur.com/IeIaWzK.jpg

Without numerical arg - error thrown

python top_pic_comments.py
Traceback (most recent call last):
File "top_pic_comments.py", line 15, in
n_pic = int( sys.argv[1] ) if sys.argv[1] else 1
IndexError: list index out of range

Made fix

With numerical arg after module name

python top_pic_comments.py 1
Title of submission:
After floods in England, swans in the street - Worcester
http://i.imgur.com/IeIaWzK.jpg

Without numerical arg

python top_pic_comments.py
Title of submission:
After floods in England, swans in the street - Worcester
http://i.imgur.com/IeIaWzK.jpg

[CamDavidsonPilon]

Thanks, @noelevans 👍