whisper : adapt to latest ggml changes

[ggerganov]

This view in the "encoder" graph of a tensor from the "conv" graph is triggering an assert with the latest build:

whisper.cpp/whisper.cpp

Line 1711 in de4d067

struct ggml_tensor * cur = ggml_view_tensor(ctx0, wstate.embd_conv);

The assert is:

whisper.cpp/ggml-alloc.c

Lines 737 to 745 in de4d067

	if (tensor->view_src != NULL) {
	if (tensor->buffer == NULL) {
	assert(tensor_alloc->offset == SIZE_MAX);
	if (tensor->view_src->buffer == NULL) {
	// this tensor was allocated without ggml-backend
	return;
	}
	ggml_backend_view_init(galloc->buffers[buffer_id], tensor);
	}

Is this a valid use case and we simply have to remove the assert, or a proper fix is necessary?

cc @slaren

[slaren]

It should still work if the assert is removed, but generally this indicates a failure to detect a change in the topology of the graph. It could probably be fixed by changing ggml_gallocr_node_needs_realloc to detect this case.

However this may indicate an issue with the graph used to reserve the buffers. What may be happening is that wstate.embd_conv was not allocated when reserving the buffers, causing it to be allocated in the graph, and then this changed to become a pre-allocated tensor. It would be better to fix that.

[ggerganov]

Fixed via 906c73b