<execution>: comment early return control flow (#849)

Fixes #818.

stl/inc/execution

@@ -1042,7 +1042,6 @@ _Common_diff_t<_InIt1, _InIt2> _Distance_min(_InIt1 _First1, const _InIt1 _Last1
     return _Result;
 }
 
-
 // PARALLEL FUNCTION TEMPLATE all_of
 template <bool _Invert, class _FwdIt, class _Pr>
 struct _Static_partitioned_all_of_family2 { // all_of/any_of/none_of task scheduled on the system thread pool
@@ -1066,6 +1065,8 @@ struct _Static_partitioned_all_of_family2 { // all_of/any_of/none_of task schedu
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
+        // GH-818: https://github.com/microsoft/STL/issues/818
 
         const auto _Range = _Basis._Get_chunk(_Key);
         for (auto _First = _Range._First; _First != _Range._Last; ++_First) {
@@ -1295,6 +1296,7 @@ struct _Static_partitioned_find2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Range     = _Basis._Get_chunk(_Key);
         const auto _This_find = _Fx(_Range._First, _Range._Last);
@@ -1500,6 +1502,7 @@ struct _Static_partitioned_find_end_backward2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Chunk_number = _Key._Chunk_number;
         const auto _Range        = _Basis._Get_chunk(_Key);
@@ -1620,6 +1623,7 @@ struct _Static_partitioned_adjacent_find2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Chunk_number = _Key._Chunk_number;
         const auto _Range        = _Basis._Get_chunk(_Key);
@@ -1835,6 +1839,7 @@ struct _Static_partitioned_mismatch2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Chunk_number = _Key._Chunk_number;
         const auto _Range1       = _Basis1._Get_chunk(_Key);
@@ -1966,6 +1971,7 @@ struct _Static_partitioned_equal2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Range1       = _Basis1._Get_chunk(_Key);
         const auto _Range2_first = _Basis2._Get_chunk(_Key)._First;
@@ -2084,6 +2090,7 @@ struct _Static_partitioned_search2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Range = _Basis._Get_chunk(_Key);
         for (auto _Candidate = _Range._First; _Candidate != _Range._Last; ++_Candidate) {
@@ -2202,6 +2209,7 @@ struct _Static_partitioned_search_n2 {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Range = _Basis._Get_chunk(_Key);
 
@@ -3054,6 +3062,7 @@ struct _Static_partitioned_is_sorted_until {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         auto _Range = _Basis._Get_chunk(_Key);
         auto _Next  = _Range._First;
@@ -3169,6 +3178,7 @@ struct _Static_partitioned_is_partitioned {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         // looking at chunks from either end, moving in towards the middle
         auto _Target_chunk_number = _Key._Chunk_number >> 1;
@@ -3281,6 +3291,7 @@ struct _Static_partitioned_is_heap_until {
         if (!_Key) {
             return _Cancellation_status::_Canceled;
         }
+        // Once _Key is obtained, the amount of work should not be discarded; see GH-818.
 
         const auto _Chunk_range_size = _Key._Size;
         const auto _Chunk_offset     = _Key._Start_at;