Fix possible hangup with CellServiceConstraint.

On phones with no SIM card, if you manage to enqueue a job with a
CellServiceConstraint, the previous check we were using to check if
there was cell service could hang indefinitely on some devices.

This changes it to a fast check, which all constraints should be.

src/org/thoughtcrime/securesms/jobmanager/impl/CellServiceConstraint.java

@@ -2,10 +2,14 @@ package org.thoughtcrime.securesms.jobmanager.impl;
 
 import android.app.Application;
 import android.app.job.JobInfo;
+import android.telephony.ServiceState;
+import android.telephony.TelephonyManager;
+
 import androidx.annotation.NonNull;
 
 import org.thoughtcrime.securesms.jobmanager.Constraint;
 import org.thoughtcrime.securesms.sms.TelephonyServiceState;
+import org.thoughtcrime.securesms.util.ServiceUtil;
 
 public class CellServiceConstraint implements Constraint {
 
@@ -24,8 +28,7 @@ public class CellServiceConstraint implements Constraint {
 
   @Override
   public boolean isMet() {
-    TelephonyServiceState telephonyServiceState = new TelephonyServiceState();
-    return telephonyServiceState.isConnected(application);
+    return CellServiceConstraintObserver.getInstance(application).hasService();
   }
 
   @Override

src/org/thoughtcrime/securesms/jobmanager/impl/CellServiceConstraintObserver.java

@@ -14,8 +14,18 @@ public class CellServiceConstraintObserver implements ConstraintObserver {
   private static final String REASON = CellServiceConstraintObserver.class.getSimpleName();
 
   private Notifier     notifier;
+  private ServiceState lastKnownState;
 
-  public CellServiceConstraintObserver(@NonNull Application application) {
+  private static CellServiceConstraintObserver instance;
+
+  public static synchronized CellServiceConstraintObserver getInstance(@NonNull Application application) {
+    if (instance == null) {
+      instance = new CellServiceConstraintObserver(application);
+    }
+    return instance;
+  }
+
+  private CellServiceConstraintObserver(@NonNull Application application) {
     TelephonyManager     telephonyManager     = (TelephonyManager) application.getSystemService(Context.TELEPHONY_SERVICE);
     ServiceStateListener serviceStateListener = new ServiceStateListener();
 
@@ -27,9 +37,15 @@ public class CellServiceConstraintObserver implements ConstraintObserver {
     this.notifier = notifier;
   }
 
+  public boolean hasService() {
+    return lastKnownState != null && lastKnownState.getState() == ServiceState.STATE_IN_SERVICE;
+  }
+
   private class ServiceStateListener extends PhoneStateListener {
     @Override
     public void onServiceStateChanged(ServiceState serviceState) {
+      lastKnownState = serviceState;
+
       if (serviceState.getState() == ServiceState.STATE_IN_SERVICE && notifier != null) {
         notifier.onConstraintMet(REASON);
       }

src/org/thoughtcrime/securesms/jobs/JobManagerFactories.java

@@ -85,7 +85,7 @@ public final class JobManagerFactories {
   }
 
   public static List<ConstraintObserver> getConstraintObservers(@NonNull Application application) {
-    return Arrays.asList(new CellServiceConstraintObserver(application),
+    return Arrays.asList(CellServiceConstraintObserver.getInstance(application),
                          new NetworkConstraintObserver(application),
                          new SqlCipherMigrationConstraintObserver());
   }