io_posix: add mapped_file::empty implementation

io_posix.cpp

@@ -63,14 +63,20 @@ mapped_file::load_fd (int mflags) {
 
 //----------------------------------------------------------------------------
 size_t
-mapped_file::size (void) const {
-    CHECK (m_size > 0);
-    CHECK (m_data != NULL);
-
+mapped_file::size (void) const
+{
     return m_size;
 }
 
 
+//-----------------------------------------------------------------------------
+bool
+mapped_file::empty (void) const
+{
+    return size () == 0;
+}
+
+
 //----------------------------------------------------------------------------
 uint8_t*
 mapped_file::data (void) {

io_posix.hpp

@@ -42,6 +42,8 @@ namespace util {
 
                 const uint8_t* data (void) const;
                 uint8_t*       data (void);
+
+                bool empty (void) const;
                 size_t size (void) const;
 
                 uint8_t*       begin (void);