Variants of %n (%+9n) still crash logger

[kguilbert]

The fix for Issue #137 fixed crashes due to %n but other variants still result in a crash. For example, %+9n causes a crash.

[mbarger99]

Tests pass on Ubuntu 16.04, but fail on Ubuntu 18.04.

[mbarger99]

Other arbitrary sequences can also trigger this that are not covered by the fix here, e.g. %In (that's a capital i, not a lowercase L). Not sure how to address this case (and other as yet undiscovered cases like this) such that it gets around the issue in all supported languages.

[mbarger99]

Testing on Ubuntu 16.04 shows that I (uppercase i), q, Z and ' (single quote) are the printable characters that are not already covered. This is likely system dependent, but going overboard here would be better than an unexpected crash.