Adds a null check in one additional location in setData

TRAC #23251

Author: Shannon Woods
Signed-off-by: Jamie Madill
Signed-off-by: Nicolas Capens
diff --git a/src/libGLESv2/renderer/BufferStorage11.cpp b/src/libGLESv2/renderer/BufferStorage11.cpp
index 87dc414..9ce7846 100644
--- a/src/libGLESv2/renderer/BufferStorage11.cpp
+++ b/src/libGLESv2/renderer/BufferStorage11.cpp
@@ -154,7 +154,7 @@
         mStagingBuffer = newStagingBuffer;
     }
 
-    if (offset != 0 || !createStagingBuffer)
+    if (data && (offset != 0 || !createStagingBuffer))
     {
         D3D11_MAPPED_SUBRESOURCE mappedResource;
         result = context->Map(mStagingBuffer, 0, D3D11_MAP_WRITE, 0, &mappedResource);