fix: GPU complex reducer prod for empty lists (#3235)

* fix: make sure that both CPU and GPU produce identical results

* fix: one more

src/awkward/_connect/cuda/cuda_kernels/awkward_reduce_prod_complex.cu

@@ -30,8 +30,8 @@ awkward_reduce_prod_complex_a(
     int64_t thread_id = blockIdx.x * blockDim.x + threadIdx.x;
 
     if (thread_id < outlength) {
-      toptr[thread_id * 2] = (T)1.0f;
-      toptr[thread_id * 2 + 1] = (T)0.0f;
+      toptr[thread_id * 2] = (T)1;
+      toptr[thread_id * 2 + 1] = (T)0;
     }
   }
 }
@@ -59,8 +59,8 @@ awkward_reduce_prod_complex_b(
 
     if (thread_id < lenparents) {
       for (int64_t stride = 1; stride < blockDim.x; stride *= 2) {
-        T real = (T)1.0f;
-        T imag = (T)0.0f;
+        T real = (T)1;
+        T imag = (T)0;
         if (idx >= stride && thread_id < lenparents && parents[thread_id] == parents[thread_id - stride]) {
           real = temp[(idx - stride) * 2];
           imag = temp[(idx - stride) * 2 + 1];