Wrong output in manual-parse in chapter 1

[tmcancode]

Because you check validateArgs() before call runCmd() so when I run command ./application -h actually to view help it always print "Must specify a number greater than 0" in the first line of output (after than is help - actually because err != nil). I think we should add condition "!c.printUsage" in validateArgs() function to sure that user want to view help not because of wrong input.

[amitsaha]

Released as part of https://github.com/practicalgo/code/releases/tag/v1.0.1