fix: raise CommandExecuted on async errors

This resolves #1224.

Previously, raising CommandExecuted for errors was dependent on the
failed result making it back to ExecuteAsync. This is not possible with
async commands, which always pass back a succesful promise result,
rather than their fulfilled result.

This change moves the event invocation for exception'd ExecuteResults to
their source, and excludes ExecuteResult from the late event invocation
in CommandService#ExecuteAsync.

src/Discord.Net.Commands/CommandService.cs

@@ -605,7 +605,7 @@ float CalculateScore(CommandMatch match, ParseResult parseResult)
             //If we get this far, at least one parse was successful. Execute the most likely overload.
             var chosenOverload = successfulParses[0];
             var result = await chosenOverload.Key.ExecuteAsync(context, chosenOverload.Value, services).ConfigureAwait(false);
-            if (!result.IsSuccess && !(result is RuntimeResult)) // succesful results raise the event in CommandInfo#ExecuteInternalAsync (have to raise it there b/c deffered execution)
+            if (!result.IsSuccess && !(result is RuntimeResult || result is ExecuteResult)) // succesful results raise the event in CommandInfo#ExecuteInternalAsync (have to raise it there b/c deffered execution)
                 await _commandExecutedEvent.InvokeAsync(chosenOverload.Key.Command, context, result);
             return result;
         }

src/Discord.Net.Commands/Info/CommandInfo.cs

@@ -274,6 +274,7 @@ private async Task<IResult> ExecuteInternalAsync(ICommandContext context, object
                 await Module.Service._cmdLogger.ErrorAsync(wrappedEx).ConfigureAwait(false);
 
                 var result = ExecuteResult.FromError(ex);
+                await Module.Service._commandExecutedEvent.InvokeAsync(this, context, result).ConfigureAwait(false);
 
                 if (Module.Service._throwOnError)
                 {