Added operator!() to smart pointers

src/TNL/DevicePointer.h

@@ -119,6 +119,12 @@ class DevicePointer< Object, Devices::Host > : public SmartPointer
          return this->pointer;
       }
 
+      __cuda_callable__
+      bool operator!() const
+      {
+         return ! this->pointer;
+      }
+
       template< typename Device = Devices::Host >
       __cuda_callable__
       const Object& getData() const
@@ -287,6 +293,12 @@ class DevicePointer< Object, Devices::Cuda > : public SmartPointer
          return this->pd;
       }
 
+      __cuda_callable__
+      bool operator!() const
+      {
+         return ! this->pd;
+      }
+
       template< typename Device = Devices::Host >
       __cuda_callable__
       const Object& getData() const

src/TNL/SharedPointer.h

@@ -167,6 +167,12 @@ class SharedPointer< Object, Devices::Host > : public SmartPointer
          return this->pd;
       }
 
+      __cuda_callable__
+      bool operator!() const
+      {
+         return ! this->pd;
+      }
+
       template< typename Device = Devices::Host >
       __cuda_callable__
       const Object& getData() const
@@ -402,6 +408,12 @@ class SharedPointer< Object, Devices::Cuda > : public SmartPointer
          return this->pd;
       }
 
+      __cuda_callable__
+      bool operator!() const
+      {
+         return ! this->pd;
+      }
+
       template< typename Device = Devices::Host >
       __cuda_callable__
       const Object& getData() const

src/TNL/UniquePointer.h

@@ -67,6 +67,12 @@ class UniquePointer< Object, Devices::Host > : public SmartPointer
          return this->pointer;
       }
 
+      __cuda_callable__
+      bool operator!() const
+      {
+         return ! this->pointer;
+      }
+
       template< typename Device = Devices::Host >
       const Object& getData() const
       {
@@ -155,6 +161,12 @@ class UniquePointer< Object, Devices::Cuda > : public SmartPointer
          return this->pd;
       }
 
+      __cuda_callable__
+      bool operator!() const
+      {
+         return ! this->pd;
+      }
+
       template< typename Device = Devices::Host >      
       const Object& getData() const
       {