mesa: don't error check the default buffer object in glBindBufferOffsetEXT()

An allocation check is already done when the buffer is created at
context creation.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
diff --git a/src/mesa/main/transformfeedback.c b/src/mesa/main/transformfeedback.c
index 07a9f9e..a075d08 100644
--- a/src/mesa/main/transformfeedback.c
+++ b/src/mesa/main/transformfeedback.c
@@ -778,12 +778,11 @@
       bufObj = ctx->Shared->NullBufferObj;
    } else {
       bufObj = _mesa_lookup_bufferobj(ctx, buffer);
-   }
-
-   if (!bufObj) {
-      _mesa_error(ctx, GL_INVALID_OPERATION,
-                  "glBindBufferOffsetEXT(invalid buffer=%u)", buffer);
-      return;
+      if (!bufObj) {
+         _mesa_error(ctx, GL_INVALID_OPERATION,
+                     "glBindBufferOffsetEXT(invalid buffer=%u)", buffer);
+         return;
+      }
    }
 
    _mesa_bind_buffer_range_xfb(ctx, obj, index, bufObj, offset, 0);