commands/exec_always: defer command on config validation
commands/exec_always: defer command on config validation

The exec_always command was executed twice, since it was not checking for the
config->validating variable.
Fix this by defering the command if the configuration is validating.

Fixes #3072

1ace/sway,SirCmpwn/sway,ascent12/sway,ascent12/sway,ascent12/sway,1ace/sway,1ace/sway