fix: empty custom text changes push no events (#8054)

# Which Problems Are Solved

If there is no custom text given, the call ends in an internal error as
no events have to be pushed.

# How the Problems Are Solved

If no events have to be pushed, no trying to push an empty list of
events.

# Additional Changes

No additional changes.

# Additional Context

Closes #6954

internal/command/instance_custom_message_text_test.go

@@ -54,7 +54,6 @@ func TestCommandSide_SetDefaultMessageText(t *testing.T) {
 				eventstore: eventstoreExpect(
 					t,
 					expectFilter(),
-					expectPush(),
 				),
 			},
 			args: args{