Print user friendly error if there is not files for uploads

[dimitrystd]

Steps

• My workspace for tests has the single xml file in the subfolder. In other words

$ ls
dir1		smartling.yml
$ ls dir1/dir11/
test.xml

• Try to upload all files

$ smartling-cli files push
panic: runtime error: slice bounds out of range

goroutine 1 [running]:
main.redactedWriter.Write(0xc420134900, 0x3, 0x4, 0xc42009a500, 0xfa, 0x100, 0x13f5a00, 0xc420298240, 0xc42003dd88)
	/go/src/cli/redacted_log.go:54 +0x2f5
main.(*redactedWriter).Write(0xc420124000, 0xc42009a500, 0xfa, 0x100, 0x0, 0x0, 0x0)
	<autogenerated>:1 +0x74
fmt.Fprintln(0x15d6e80, 0xc420124000, 0xc42003dd88, 0x1, 0x1, 0x37, 0x0, 0x0)
	/usr/local/go/src/fmt/print.go:248 +0x8b
main.reportError(0x15d85c0, 0xc420134b00)
	/go/src/cli/main.go:240 +0xbf
main.main()
	/go/src/cli/main.go:232 +0x3ea

• Ok, try to upload files by mask

$ smartling-cli files push *.xml
panic: runtime error: slice bounds out of range

goroutine 1 [running]:
main.redactedWriter.Write(0xc420106900, 0x3, 0x4, 0xc420182120, 0x87, 0x90, 0x13f5a00, 0xc420284300, 0xc42003dd88)
	/go/src/cli/redacted_log.go:54 +0x2f5
main.(*redactedWriter).Write(0xc420102020, 0xc420182120, 0x87, 0x90, 0x0, 0x0, 0x0)
	<autogenerated>:1 +0x74
fmt.Fprintln(0x15d6e80, 0xc420102020, 0xc42003dd88, 0x1, 0x1, 0x37, 0x0, 0x0)
	/usr/local/go/src/fmt/print.go:248 +0x8b
main.reportError(0x15d85c0, 0xc420106b00)
	/go/src/cli/main.go:240 +0xbf
main.main()
	/go/src/cli/main.go:232 +0x3ea

• Finally, try to upload with valid mask

$ smartling-cli files push **/*.xml
dir1/dir11/test.xml (xml) new [1 strings 27 words]

This is what i expected before

DoD:
For the first to 2 examples, i would like to see something like There are no files to upload