document error for kernel enqueue with a work-group size of zero (KhronosGroup#1542)

Author: bashbaug

api/opencl_runtime_layer.asciidoc

@@ -12149,6 +12149,7 @@ Otherwise, it returns one of the following errors:
     {size_t_TYPE} on the device associated with _command_queue_
   * {CL_INVALID_WORK_GROUP_SIZE}
     ** if _local_work_size_ is not `NULL`, if the work-group size must be uniform, and if the _global_work_size_ is not evenly divisible by the _local_work_size_
+    ** if _local_work_size_ is not `NULL` and if the total number of work-items in the work-group is zero
     ** if _local_work_size_ is not `NULL` and if the total number of work-items in the work-group is greater than the maximum work-group size supported for _kernel_ on the device associated with _command_queue_ (is greater than the value returned for {CL_KERNEL_WORK_GROUP_SIZE})
     ** if _local_work_size_ is not `NULL` and if the _local_work_size_ does not match the required work-group size for _kernel_
     ** if _local_work_size_ is not `NULL` and if the _local_work_size_ is not consistent with the required number of sub-groups for _kernel_