ExportWriter fails with max values for fields

TestExportWriter.testMultipleSorts has been hanging and epugh shared this seed that reproduced:

./gradlew :solr:core:test --tests “org.apache.solr.handler.export.TestExportWriter.testMultipleSorts” -Ptests.jvms=4 “-Ptests.jvmargs=-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=120m” -Ptests.seed=9ED4BC2C416D56E9 -Ptests.file.encoding=US-ASCI

https://lists.apache.org/list?builds@solr.apache.org:lte=1y:&header_body=org.apache.solr.handler.export.TestExportWriter.testMultipleSorts

Looking into the failure found that if Float.MAX_VALUE is chosen and document ends up being compared to the top doc. That document will get skipped since MAX_VALUE can't be more than MAX_VALUE.

This causes the export writer to hang looking for more documents indefinitely until the test framework times out.