[rrd4j] Improved the interpolation workaround (openhab#17437)

Signed-off-by: Jörg Sautter <[email protected]>

Author: joerg1985

bundles/org.openhab.persistence.rrd4j/src/main/java/org/openhab/persistence/rrd4j/internal/RRD4jPersistenceService.java

@@ -373,7 +373,7 @@ private synchronized void writePointToDatabase(String name, double value, long t
                 if (timestamp - 1 > db.getLastUpdateTime()) {
                     // only do it if there is not already a value
                     double lastValue = db.getLastDatasourceValue(DATASOURCE_STATE);
-                    if (!Double.isNaN(lastValue)) {
+                    if (!Double.isNaN(lastValue) && lastValue != value) {
                         Sample sample = db.createSample();
                         sample.setTime(timestamp - 1);
                         sample.setValue(DATASOURCE_STATE, lastValue);