Added wxMemoryBuffer::Clear() and IsEmpty() methods.

Add two convenient methods which may be used instead of testing or setting the
buffer length.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70407 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/buffer.h

@@ -309,6 +309,17 @@ public:
     */
     void AppendData(const void *data, size_t len);
 
+    /**
+        Clear the buffer contents.
+
+        The buffer won't contain any data after this method is called.
+
+        @see IsEmpty()
+
+        @since 2.9.4
+     */
+    void Clear();
+
     /**
         Ensure that the buffer is big enough and return a pointer to the start
         of the empty space in the buffer. This pointer can be used to directly
@@ -343,6 +354,15 @@ public:
     */
     void* GetWriteBuf(size_t sizeNeeded);
 
+    /**
+        Returns true if the buffer contains no data.
+
+        @see Clear()
+
+        @since 2.9.4
+     */
+    bool IsEmpty() const;
+
     /**
         Ensures the buffer has at least @a size bytes available.
     */