When looking for double colon len(line) is longer then 1.

Addresses GH-5116.

It comes up that when parsing json that if you are missing the last double quote on the last variable and the next line is just '}' we will get an out of range error. In this instance we will also then make sure that the line is long enough to have two colons.
Merge pull request #6197 from risaacson/issues_5116

When looking for double colon len(line) must be longer then 1.