Fix bad indentation calculation in the console reporter

The problem came from the console reporter trying to provide a
fancy linebreaking (primarily for things like `SCENARIO` or the
BDD macros), so that new lines start with extra indentation if
the text being line broken starts as "{text}: ".

The console reporter did not properly take into account cases
where the ": " part would already be in a later line, in which
case it would ask for non-sensical level of indentation (larger
than single line length).

We fixed this by also enforcing that the special indentation case
only triggers if the ": " is found early enough in the line, so
that we also avoid degenerate cases like this:
```
blablabla: F
           a
           n
           c
           y
           .
           .
           .
```

Fixes #2309

tests/SelfTest/Baselines/automake.sw.approved.txt

@@ -191,6 +191,7 @@ Nor would this
 :test-result: FAIL Regex string matcher
 :test-result: PASS Regression test #1
 :test-result: PASS Reporter's write listings to provided stream
+:test-result: PASS Reproducer for #2309 - a very long description past 80 chars (default console width) with a late colon : blablabla
 :test-result: PASS SUCCEED counts as a test pass
 :test-result: PASS SUCCEED does not require an argument
 :test-result: PASS Scenario: BDD tests requiring Fixtures to provide commonly-accessed data or methods