fixed findbugs problem

src/main/java/it/unibz/inf/isochrone/config/ConfigIsochrone.java

@@ -10,6 +10,7 @@ import com.tngtech.configbuilder.annotation.valueextractor.PropertyValue;
 
 import it.unibz.inf.isochrone.db.ConnectionFactory;
 
+import java.sql.CallableStatement;
 import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;
@@ -183,8 +184,10 @@ public final class ConfigIsochrone {
 		final String query = "SELECT tablename FROM pg_tables WHERE schemaname='public'";
 
 		ResultSet rs = null;
+		CallableStatement stmt = null;
 		try {
-			rs = getConnection().prepareCall(query).executeQuery();
+			stmt = getConnection().prepareCall(query);
+			rs = stmt.executeQuery();
 			while (rs.next()) {
 				result.add(rs.getString("tablename"));
 			}
@@ -192,6 +195,7 @@ public final class ConfigIsochrone {
 			LOGGER.warn("Could not get tables from database");
 		} finally {
 			DbUtils.closeQuietly(rs);
+			DbUtils.closeQuietly(stmt);
 		}
 
 		return result;