Don't crash on a null pointer passed to glBufferData

TRAC #11528

 * Initialise buffer to 0 if BufferData is called with data = NULL
   (special case: if not resizing, just leave the old data in place).
 * BufferSubData ignores calls with data = NULL
 * Replace Buffer::data_t with GLubyte.

Author:    Andrew Lewycky
Signed-off-by: Shannon Woods
Signed-off-by: Daniel Koch

git-svn-id: https://angleproject.googlecode.com/svn/trunk@59 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/src/libGLESv2/libGLESv2.cpp b/src/libGLESv2/libGLESv2.cpp
index fcb8633..cb38dc3 100644
--- a/src/libGLESv2/libGLESv2.cpp
+++ b/src/libGLESv2/libGLESv2.cpp
@@ -482,6 +482,11 @@
             return error(GL_INVALID_VALUE);
         }
 
+        if (data == NULL)
+        {
+            return;
+        }
+
         gl::Context *context = gl::getContext();
 
         if (context)