Only valid `collectors` should be taken into account when computing the `scoreMode` in `MultiCollector`

[kkewwei]

Description

During the retrieval of collectors via collector.getLeafCollector(context), some invocations may throw a CollectionTerminatedException-indicating this leaf collector does not need this segment. However, when computing scoreMode(), we still factor in collectors that throw such exceptions, which seems logically inconsistent.

lucene/lucene/core/src/java/org/apache/lucene/search/MultiCollector.java

Line 124 in 424ef9d

public LeafCollector getLeafCollector(LeafReaderContext context) throws IOException {

I'm pleasure to fix it.