[Darwin] Some MTRDevice mtr_strongify sites need to guard against nil self (project-chip#36131)

* [Darwin] Some MTRDevice mtr_strongify sites need to guard against nil self

* Took ksperling-apple's suggestion to use VerifyOrReturn instead for cleaner code

Author: jtung-apple

src/darwin/Framework/CHIP/MTRDevice_Concrete.mm

@@ -389,6 +389,8 @@ - (instancetype)initWithNodeID:(NSNumber *)nodeID controller:(MTRDeviceControlle
             mtr_weakify(self);
             _systemTimeChangeObserverToken = [[NSNotificationCenter defaultCenter] addObserverForName:NSSystemClockDidChangeNotification object:nil queue:nil usingBlock:^(NSNotification * _Nonnull notification) {
                 mtr_strongify(self);
+                VerifyOrReturn(self);
+
                 std::lock_guard lock(self->_lock);
                 [self _resetStorageBehaviorState];
             }];
@@ -760,6 +762,8 @@ - (void)_ensureSubscriptionForExistingDelegates:(NSString *)reason
             mtr_weakify(self);
             [self _scheduleSubscriptionPoolWork:^{
                 mtr_strongify(self);
+                VerifyOrReturn(self);
+
                 [self->_deviceController asyncDispatchToMatterQueue:^{
                     std::lock_guard lock(self->_lock);
                     [self _setupSubscriptionWithReason:[NSString stringWithFormat:@"%@ and scheduled subscription is happening", reason]];
@@ -1168,16 +1172,16 @@ - (void)_scheduleSubscriptionPoolWork:(dispatch_block_t)workBlock inNanoseconds:
     mtr_weakify(self);
     dispatch_block_t workBlockToQueue = ^{
         mtr_strongify(self);
-        if (nil == self) {
-            // This block may be delayed by a specified number of nanoseconds, potentially running after the device is deallocated.
-            // If so, MTRAsyncWorkItem::initWithQueue will assert on a nil queue, which will cause a crash.
-            return;
-        }
+        // This block may be delayed by a specified number of nanoseconds, potentially running after the device is deallocated.
+        // If so, MTRAsyncWorkItem::initWithQueue will assert on a nil queue, which will cause a crash.
+        VerifyOrReturn(self);
 
         // In the case where a resubscription triggering event happened and already established, running the work block should result in a no-op
         MTRAsyncWorkItem * workItem = [[MTRAsyncWorkItem alloc] initWithQueue:self.queue];
         [workItem setReadyHandler:^(id _Nonnull context, NSInteger retryCount, MTRAsyncWorkCompletionBlock _Nonnull completion) {
             mtr_strongify(self);
+            VerifyOrReturn(self);
+
             MTR_LOG("%@ - work item is ready to attempt pooled subscription", self);
             os_unfair_lock_lock(&self->_lock);
 #ifdef DEBUG
@@ -1257,6 +1261,8 @@ - (void)_handleResubscriptionNeededWithDelayOnDeviceQueue:(NSNumber *)resubscrip
     mtr_weakify(self);
     auto resubscriptionBlock = ^{
         mtr_strongify(self);
+        VerifyOrReturn(self);
+
         [self->_deviceController asyncDispatchToMatterQueue:^{
             [self _triggerResubscribeWithReason:@"ResubscriptionNeeded timer fired" nodeLikelyReachable:NO];
         } errorHandler:^(NSError * _Nonnull error) {
@@ -1369,6 +1375,8 @@ - (void)_doHandleSubscriptionReset:(NSNumber * _Nullable)retryDelay
     mtr_weakify(self);
     auto resubscriptionBlock = ^{
         mtr_strongify(self);
+        VerifyOrReturn(self);
+
         [self->_deviceController asyncDispatchToMatterQueue:^{
             std::lock_guard lock(self->_lock);
             [self _reattemptSubscriptionNowIfNeededWithReason:@"got subscription reset"];
@@ -2386,9 +2394,9 @@ - (void)_setupSubscriptionWithReason:(NSString *)reason
         mtr_weakify(self);
         dispatch_after(dispatch_time(DISPATCH_TIME_NOW, static_cast<int64_t>(kSecondsToWaitBeforeMarkingUnreachableAfterSettingUpSubscription) * static_cast<int64_t>(NSEC_PER_SEC)), self.queue, ^{
             mtr_strongify(self);
-            if (self != nil) {
-                [self _markDeviceAsUnreachableIfNeverSubscribed];
-            }
+            VerifyOrReturn(self);
+
+            [self _markDeviceAsUnreachableIfNeverSubscribed];
         });
     }
 
@@ -3242,6 +3250,8 @@ - (void)_checkExpiredExpectedValues
         mtr_weakify(self);
         dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t) (waitTime * NSEC_PER_SEC)), self.queue, ^{
             mtr_strongify(self);
+            VerifyOrReturn(self);
+
             [self _performScheduledExpirationCheck];
         });
     }