Combine semantics for empty bundle for min, max is wrong

The combine semantics for Min for empty bundles is to emit MAX_INT, if using global windows. Our implementation currently deviates from java, because we use binary combiners (and thus emit the default element for the type (0).

Ditto for the other binary combiners in stats.

Imported from Jira [BEAM-3296](https://issues.apache.org/jira/browse/BEAM-3296). Original Jira may contain additional context.
Reported by: herohde.

Start by locating the stats binary combiners and inspect how empty bundles are handled for Min, Max, and the other combiners. Compare their identities with the Java semantics described in the issue, then add or update tests showing the expected empty-bundle results for each affected combiner.

Written by the indexing model from the issue text.