[Bugfix] Fix chunked prefill for GGUF (#14666)

Signed-off-by: SzymonOzog <szymon.ozog@aleph-alpha.com>

Author: SzymonOzog

vllm/model_executor/layers/quantization/gguf.py

@@ -98,6 +98,13 @@ def get_quant_method(self, layer: torch.nn.Module,
 
 def _fuse_mul_mat(x: torch.Tensor, qweight: torch.Tensor,
                   qweight_type: int) -> torch.Tensor:
+    # HACK: when doing chunked prefill we don't generate output tokens
+    # so input to logits generator is empty which causes invalid parameter
+    if x.shape[0] == 0:
+        return torch.empty(x.shape[0],
+                           qweight.shape[0],
+                           dtype=x.dtype,
+                           device=x.device)
     # there is no need to call any kernel for fp16/bf16
     if qweight_type in UNQUANTIZED_TYPES:
         return x @ qweight.T