Fix memory releasing in vector

Memory (buffer) should be released if capacity is greater
than zero (which means that something was allocated), not if size
is greater than zero.

Author: jszuppe

include/boost/compute/container/vector.hpp

@@ -293,8 +293,8 @@ class vector
     /// Move-assigns the data from \p other to \c *this.
     vector& operator=(vector&& other)
     {
-        if(m_size){
-            m_allocator.deallocate(m_data, m_size);
+        if(capacity() > 0){
+            m_allocator.deallocate(m_data, capacity());
         }
 
         m_data = std::move(other.m_data);
@@ -310,8 +310,8 @@ class vector
     /// Destroys the vector object.
     ~vector()
     {
-        if(m_size){
-            m_allocator.deallocate(m_data, m_size);
+        if(capacity() > 0){
+            m_allocator.deallocate(m_data, capacity());
         }
     }
 
@@ -401,11 +401,14 @@ class vector
                     )
                 );
 
-            // copy old values to the new buffer
-            ::boost::compute::copy(m_data, m_data + m_size, new_data, queue);
+            if(capacity() > 0)
+            {
+                // copy old values to the new buffer
+                ::boost::compute::copy(m_data, m_data + m_size, new_data, queue);
 
-            // free old memory
-            m_allocator.deallocate(m_data, m_size);
+                // free old memory
+                m_allocator.deallocate(m_data, capacity());
+            }
 
             // set new data and size
             m_data = new_data;
@@ -430,6 +433,10 @@ class vector
     /// Returns the capacity of the vector.
     size_type capacity() const
     {
+        if(m_data == pointer()) // null pointer check
+        {
+            return 0;
+        }
         return m_data.get_buffer().size() / sizeof(T);
     }
 
@@ -447,11 +454,14 @@ class vector
                     )
                 );
 
-            // copy old values to the new buffer
-            ::boost::compute::copy(m_data, m_data + m_size, new_data, queue);
+            if(capacity() > 0)
+            {
+                // copy old values to the new buffer
+                ::boost::compute::copy(m_data, m_data + m_size, new_data, queue);
 
-            // free old memory
-            m_allocator.deallocate(m_data, m_size);
+                // free old memory
+                m_allocator.deallocate(m_data, capacity());
+            }
 
             // set new data
             m_data = new_data;