fix(ui): select a predictable first table on startup

previously map.values.iterator.next was selecting a random table

src/main/engine/net/sf/jailer/datamodel/DataModel.java

@@ -37,11 +37,13 @@ import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Optional;
 import java.util.Set;
 import java.util.SortedSet;
 import java.util.TreeMap;
 import java.util.TreeSet;
 
+import org.apache.commons.collections4.MapUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -304,6 +306,18 @@ public class DataModel {
 		return tables.values();
 	}
 
+  /**
+   * When starting UI we need to pick a table to get selected at first, in a stable way.
+   * Alphabetically first table sounds good and deterministic.
+   */
+  public Optional<Table> firstTable() {
+    if (MapUtils.isEmpty(tables)) {
+      return Optional.empty();
+    }
+
+    return tables.keySet().stream().sorted().findFirst().map(tables::get);
+  }
+
 	/**
 	 * Reads in <code>table.csv</code> and <code>association.csv</code>
 	 * and builds the relational data model.

src/main/engine/net/sf/jailer/extractionmodel/ExtractionModel.java

@@ -198,7 +198,7 @@ public class ExtractionModel {
 	public ExtractionModel(DataModel dataModel, ExecutionContext executionContext) {
 		this.dataModel = dataModel;
 		this.version = null;
-		subject = dataModel.getTables().iterator().hasNext()? dataModel.getTables().iterator().next() : null;
+		subject = dataModel.firstTable().orElse(null);
 		condition = "";
 		dataModel.setRestrictionModel(new RestrictionModel(dataModel, executionContext));
 		dataModel.deriveFilters();