Split sentence should ignore decimal numbers

[raineorshine]

An unanticipated edge case for #3354.

Steps to Reproduce

A - B 1.1

1. Activate Split Sentence.
2. Activate Split Sentence again.

Current Behavior

Do nothing and alert the user that it is not possible.

Expected Behavior

The first activation should split in "-".

The second activation should do nothing and alert the user that it is not possible.

Note that this should only be handled this way for decimal numbers, not 'a.a', which should split as usual.

Test

Add an appropriate test case.