Properly handle empty args with new shellquote lib

Fixes #1454

internal/shell/shell.go

@@ -2,6 +2,7 @@ package shell
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -36,6 +37,9 @@ func RunCommand(input string) (string, error) {
 	if err != nil {
 		return "", err
 	}
+	if len(args) == 0 {
+		return "", errors.New("No arguments")
+	}
 	inputCmd := args[0]
 
 	return ExecCommand(inputCmd, args[1:]...)
@@ -49,6 +53,9 @@ func RunBackgroundShell(input string) (func() string, error) {
 	if err != nil {
 		return nil, err
 	}
+	if len(args) == 0 {
+		return nil, errors.New("No arguments")
+	}
 	inputCmd := args[0]
 	return func() string {
 		output, err := RunCommand(input)
@@ -72,6 +79,9 @@ func RunInteractiveShell(input string, wait bool, getOutput bool) (string, error
 	if err != nil {
 		return "", err
 	}
+	if len(args) == 0 {
+		return "", errors.New("No arguments")
+	}
 	inputCmd := args[0]
 
 	// Shut down the screen because we're going to interact directly with the shell