LineageSettingsService: prevent setting net.hostname to null

If the user did not set a custom hostname, the settings service will
set net.hostname to null.

Only set net.hostname if the user actually set a custom hostname.

Change-Id: Ie9cc84e5e8c9468a7e698896e2b21c14a37ebffc
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>

lineage/lib/main/java/org/lineageos/platform/internal/LineageSettingsService.java

@@ -45,7 +45,9 @@ public class LineageSettingsService extends LineageSystemService {
             // Load custom hostname
             String hostname = LineageSettings.Secure.getString(mContext.getContentResolver(),
                     LineageSettings.Secure.DEVICE_HOSTNAME);
-            SystemProperties.set("net.hostname", hostname);
+            if (hostname != null) {
+                SystemProperties.set("net.hostname", hostname);
+            }
         }
     }