fix clang analyzer "error: Called C++ object pointer is null" error

Author: serges147

include/libcyphal/presentation/client.hpp

@@ -92,11 +92,13 @@ class ClientBase
 
     ClientBase& operator=(ClientBase&& other) noexcept
     {
-        CETL_DEBUG_ASSERT(shared_client_ != nullptr, "Not supposed to move construct to already moved `this`.");
         CETL_DEBUG_ASSERT(other.shared_client_ != nullptr,
                           "Not supposed to move construct from already moved `other`.");
 
-        (void) shared_client_->release();
+        if (nullptr != shared_client_)
+        {
+            (void) shared_client_->release();
+        }
 
         shared_client_ = std::exchange(other.shared_client_, nullptr);
         priority_      = other.priority_;

include/libcyphal/presentation/publisher.hpp

@@ -78,10 +78,12 @@ class PublisherBase
 
     PublisherBase& operator=(PublisherBase&& other) noexcept
     {
-        CETL_DEBUG_ASSERT(impl_ != nullptr, "Not supposed to move to already moved `this`.");
         CETL_DEBUG_ASSERT(other.impl_ != nullptr, "Not supposed to move from already moved `other`.");
 
-        (void) impl_->release();
+        if (nullptr != impl_)
+        {
+            (void) impl_->release();
+        }
 
         impl_     = std::exchange(other.impl_, nullptr);
         priority_ = other.priority_;

include/libcyphal/presentation/subscriber.hpp

@@ -50,9 +50,12 @@ class SubscriberBase : public SubscriberImpl::CallbackNode
 
     SubscriberBase& operator=(SubscriberBase&& other) noexcept
     {
-        CETL_DEBUG_ASSERT(impl_ != nullptr, "Not supposed to move to already moved `this`.");
+        CETL_DEBUG_ASSERT(other.impl_ != nullptr, "Not supposed to move from already moved `other`.");
 
-        impl_->releaseCallbackNode(*this);
+        if (nullptr != impl_)
+        {
+            impl_->releaseCallbackNode(*this);
+        }
 
         impl_ = std::exchange(other.impl_, nullptr);