Fix incomplete operation errors

[smeyer198]

IncompleteOperationErrors are reported, if the a dataflow path does not end in an accepting state. However, if there are multiple dataflow paths, multiple IncompleteOperationErrors are reported, although some paths lead to an accepting state. For example, for

Cipher c = Cipher.getInstance([...]);
c.init([...]);
if (Math.random() > 0.5) {
    c.doFinal([...]);
}

the analysis reports an error at the call to init with the info that a call to doFinal is missing, and it reports an error at the call to doFinal with the info that a call to doFinal is missing. The second error is not quite correct because doFinal is called on the corresponding dataflow path. Hence, this is a false positive.
This PR adds the logic for reporting the errors only on the correct positions (here at init) and adds the information that there is a potential dataflow path, where a call to doFinal is missing. This holds also for loops.

Fixes #51