Update HomematicDeviceDiscoveryService.java (openhab#11971)

fix for bug openhab#11969

After a restart of openHAB the function 'getScanTimeout()' is called before the member 'installModeDuration' has been initialized with the correct value from the configuration. With a large number of Homematic devices, the default value of 'installModeDuration' is too small to read in all Homematic devices from the CCU.
Therefore, when calling the function 'getScanTimeout()', the value is read directly from the configuration. The member 'installModeDuration' has been removed.

Signed-off-by: raykleibelt <54982000+raykleibelt@users.noreply.github.com>
Signed-off-by: Nick Waterton <n.waterton@outlook.com>

bundles/org.openhab.binding.homematic/src/main/java/org/openhab/binding/homematic/internal/discovery/HomematicDeviceDiscoveryService.java

@@ -52,7 +52,6 @@ public class HomematicDeviceDiscoveryService extends AbstractDiscoveryService
     private Future<?> loadDevicesFuture;
     private volatile boolean isInInstallMode = false;
     private volatile Object installModeSync = new Object();
-    private volatile int installModeDuration = HomematicConfig.DEFAULT_INSTALL_MODE_DURATION;
 
     public HomematicDeviceDiscoveryService() {
         super(Collections.singleton(new ThingTypeUID(BINDING_ID, "-")), DISCOVER_TIMEOUT_SECONDS, false);
@@ -103,10 +102,9 @@ private void enableInstallMode() {
             if (bridgeHandler != null) {
                 Thing bridge = bridgeHandler.getThing();
                 bridgeStatus = bridge.getStatus();
-                updateInstallModeDuration(bridge);
             }
             if (ThingStatus.ONLINE == bridgeStatus) {
-                gateway.setInstallMode(true, installModeDuration);
+                gateway.setInstallMode(true, getInstallModeDuration());
 
                 int remaining = gateway.getInstallMode();
                 if (remaining > 0) {
@@ -123,14 +121,16 @@ private void enableInstallMode() {
         }
     }
 
-    private void updateInstallModeDuration(Thing bridge) {
-        HomematicConfig config = bridge.getConfiguration().as(HomematicConfig.class);
-        installModeDuration = config.getInstallModeDuration();
+    private int getInstallModeDuration() {
+        if (bridgeHandler != null) {
+            return bridgeHandler.getThing().getConfiguration().as(HomematicConfig.class).getInstallModeDuration();
+        }
+        return HomematicConfig.DEFAULT_INSTALL_MODE_DURATION;
     }
 
     @Override
     public int getScanTimeout() {
-        return installModeDuration;
+        return getInstallModeDuration();
     }
 
     @Override