Prevent zero radius in BaseXYPointTestCase

[iverase]

Fixes the following CI error:

TestXYPointQueries > testRandomMedium {seed=[3C55FEBBB310DF4C:818BC913F275BC2A]} FAILED
    java.lang.IllegalArgumentException: radius must be bigger than 0, got 0.0
        at __randomizedtesting.SeedInfo.seed([3C55FEBBB310DF4C:818BC913F275BC2A]:0)
        at org.apache.lucene.geo.XYCircle.<init>(XYCircle.java:46)
        at org.apache.lucene.document.XYPointField.newDistanceQuery(XYPointField.java:178)
        at org.apache.lucene.search.TestXYPointQueries.newDistanceQuery(TestXYPointQueries.java:39)
        at org.apache.lucene.tests.geo.BaseXYPointTestCase.verifyRandomDistances(BaseXYPointTestCase.java:932)
        at org.apache.lucene.tests.geo.BaseXYPointTestCase.verify(BaseXYPointTestCase.java:792)
        at org.apache.lucene.tests.geo.BaseXYPointTestCase.doTestRandom(BaseXYPointTestCase.java:761)
        at org.apache.lucene.tests.geo.BaseXYPointTestCase.testRandomMedium(BaseXYPointTestCase.java:673)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)

[github-actions]

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[dweiss]

Thank you, @iverase