Do not invoke bulk_chunked for zero shape (NVIDIA#2210)

* Fix bulk_chunked zero shape

* Format bulk chunked changes

Author: fallintoplace

include/stdexec/__detail/__bulk.hpp

@@ -281,7 +281,10 @@ namespace STDEXEC
 
           STDEXEC_TRY
           {
-            __state.__data_.__fun_(__shape_t(), __shape_t(__state.__data_.__shape_), __args...);
+            if (__shape_t{} < __state.__data_.__shape_)
+            {
+              __state.__data_.__fun_(__shape_t(), __shape_t(__state.__data_.__shape_), __args...);
+            }
             STDEXEC::set_value(static_cast<_State&&>(__state).__rcvr_,
                                static_cast<_Args&&>(__args)...);
           }

test/stdexec/algos/adaptors/test_bulk.cpp

@@ -701,6 +701,26 @@ namespace
     ex::start(op);
   }
 
+  TEST_CASE("bulk_chunked function is not called with a zero shape", "[adaptors][bulk]")
+  {
+    int called{};
+
+    auto snd = ex::just() | ex::bulk_chunked(ex::seq, 0, [&called](int, int) { called++; });
+    ex::sync_wait(std::move(snd));
+
+    CHECK(called == 0);
+  }
+
+  TEST_CASE("bulk_chunked function is not called with a negative shape", "[adaptors][bulk]")
+  {
+    int called{};
+
+    auto snd = ex::just() | ex::bulk_chunked(ex::seq, -1, [&called](int, int) { called++; });
+    ex::sync_wait(std::move(snd));
+
+    CHECK(called == 0);
+  }
+
   TEST_CASE("bulk_unchunked function in not called on stop", "[adaptors][bulk]")
   {
     constexpr int n = 2;