Avoid 2 more RSS Expanded finder pattern false positive scenarios

[gredler]

This PR addresses 2 additional finder pattern false positive scenarios found during fuzz testing Okapi encode + ZXing decode of RSS Expanded (DataBar Expanded).

First, a finder pattern false positive can easily lead to an error decoding the data character to the left of the finder pattern. When this happens, it is better to continue searching for the real finder pattern, instead of giving up completely.

Second, we can detect additional false positives by relying on the mathematical relationship between the widths of the finder patterns and the space between them, making sure that the position of the finder pattern is somewhat near where we would expect to find it, relative to the previous finder pattern.

This PR includes two additional test cases, one for each scenario addressed.