Update usage of the error buffer following changes in the protocol.

theano/sandbox/gpuarray/subtensor.py

@@ -832,6 +832,8 @@ __device__ ga_half atomicAdd(ga_half *addr, ga_half val) {
               }
               if (kerr != 0) {
                 PyErr_SetString(PyExc_IndexError, "Index out of bounds");
+                kerr = 0;
+                py_self->ga.ops->buffer_write(errbuf, 0, &kerr, sizeof(int));
                 return 1;
               }
             }