gmio_core: force size to 0 for NULL buffer

src/gmio_core/buffer.c

@@ -35,7 +35,7 @@ gmio_buffer_t gmio_buffer(void* ptr, size_t size)
 {
     gmio_buffer_t buff;
     buff.ptr = ptr;
-    buff.size = size;
+    buff.size = ptr != NULL ? size : 0;
     buff.deallocate_func = NULL;
     return buff;
 }

src/gmio_core/buffer.h

@@ -40,7 +40,10 @@ typedef struct gmio_buffer gmio_buffer_t;
 
 GMIO_C_LINKAGE_BEGIN
 
-/*! Returns an initialized gmio_buffer object */
+/*! Returns an initialized gmio_buffer object
+ *
+ *  If \p ptr is NULL then gmio_buffer::size is forced to \c 0
+ */
 GMIO_LIB_EXPORT gmio_buffer_t gmio_buffer(void* ptr, size_t size);
 
 /*! Returns a gmio_buffer object allocated with standard malloc() */