fix kernel backend select bug (#41002)

paddle/phi/api/lib/kernel_dispatch.cc

@@ -25,6 +25,7 @@ namespace experimental {
 namespace detail {
 
 BackendSet GetTensorBackendSet(const phi::TensorBase& t) {
+  if (t.initialized()) {
     BackendSet backend_set(phi::TransToPhiBackend(t.place()));
     switch (t.layout()) {
       case DataLayout::MKLDNN:
@@ -35,6 +36,8 @@ BackendSet GetTensorBackendSet(const phi::TensorBase& t) {
         break;
     }
     return backend_set;
+  }
+  return BackendSet(Backend::UNDEFINED);
 }
 
 std::size_t CountLeadingZeros(uint64_t val) {