Dont crash if channelz not initialized (#27435)

* Dont crash if channelz not initialized

* Automated change: Fix sanity tests

* review feedback

Co-authored-by: ctiller <ctiller@users.noreply.github.com>

src/core/ext/filters/client_channel/client_channel.cc

@@ -456,6 +456,7 @@ class ClientChannel::SubchannelWrapper : public SubchannelInterface {
               chand, this, subchannel_.get());
     }
     GRPC_CHANNEL_STACK_REF(chand_->owning_stack_, "SubchannelWrapper");
+    if (chand_->channelz_node_ != nullptr) {
       auto* subchannel_node = subchannel_->channelz_node();
       if (subchannel_node != nullptr) {
         auto it = chand_->subchannel_refcount_map_.find(subchannel_.get());
@@ -466,6 +467,7 @@ class ClientChannel::SubchannelWrapper : public SubchannelInterface {
         }
         ++it->second;
       }
+    }
     chand_->subchannel_wrappers_.insert(this);
   }
 
@@ -476,16 +478,19 @@ class ClientChannel::SubchannelWrapper : public SubchannelInterface {
               chand_, this, subchannel_.get());
     }
     chand_->subchannel_wrappers_.erase(this);
+    if (chand_->channelz_node_ != nullptr) {
       auto* subchannel_node = subchannel_->channelz_node();
       if (subchannel_node != nullptr) {
         auto it = chand_->subchannel_refcount_map_.find(subchannel_.get());
         GPR_ASSERT(it != chand_->subchannel_refcount_map_.end());
         --it->second;
         if (it->second == 0) {
-        chand_->channelz_node_->RemoveChildSubchannel(subchannel_node->uuid());
+          chand_->channelz_node_->RemoveChildSubchannel(
+              subchannel_node->uuid());
           chand_->subchannel_refcount_map_.erase(it);
         }
       }
+    }
     GRPC_CHANNEL_STACK_UNREF(chand_->owning_stack_, "SubchannelWrapper");
   }