FOP-3349: A line that overflows on the float re-layout pass is reported, not a NullPointerException

[plutext]

Fixes FOP-3349.

LineLayoutManager.LineBreakingAlgorithm.updateData2 reports a line that does not fit through curChildLM:

if (curChildLM.getFObj() == null) {
    eventProducer.lineOverflows(this, getFObj().getName(), ...);
} else {
    eventProducer.lineOverflows(this, curChildLM.getFObj().getName(), ...);
}

On the float re-layout pass (PageBreaker.handleFloatLayout), curChildLM is null. A line that overflows there,
beside a float wider than the measure, threw a NullPointerException, and the document failed instead of the
overflow being reported.

The change. Test curChildLM == null as well as getFObj() == null, so the overflow is reported against the
line manager's own FO, as it already is when the child has no FO. The code only reports; layout does not change.

Test. float_overflow_relayout.xml: a 480pt float in a 425pt region, then a block with an overflowing word.
It throws the NullPointerException without the change. With it, the fop-core suite passes, 3662 tests and 0
failures, and checkstyle reports 0 violations.

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