Avoid redundant string splits

There likely isn't actually more than once to split in the source
strings in these cases, but avoid doing so anyway as we're only
interested in the first.

args.go

@@ -54,7 +54,7 @@ func OnlyValidArgs(cmd *Command, args []string) error {
 		// A description is following a tab character.
 		var validArgs []string
 		for _, v := range cmd.ValidArgs {
-			validArgs = append(validArgs, strings.Split(v, "\t")[0])
+			validArgs = append(validArgs, strings.SplitN(v, "\t", 2)[0])
 		}
 		for _, v := range args {
 			if !stringInSlice(v, validArgs) {

bash_completions.go

@@ -621,7 +621,7 @@ func writeRequiredNouns(buf io.StringWriter, cmd *Command) {
 	for _, value := range cmd.ValidArgs {
 		// Remove any description that may be included following a tab character.
 		// Descriptions are not supported by bash completion.
-		value = strings.Split(value, "\t")[0]
+		value = strings.SplitN(value, "\t", 2)[0]
 		WriteStringAndCheck(buf, fmt.Sprintf("    must_have_one_noun+=(%q)\n", value))
 	}
 	if cmd.ValidArgsFunction != nil {

completions.go

@@ -226,14 +226,14 @@ func (c *Command) initCompleteCmd(args []string) {
 				}
 				if noDescriptions {
 					// Remove any description that may be included following a tab character.
-					comp = strings.Split(comp, "\t")[0]
+					comp = strings.SplitN(comp, "\t", 2)[0]
 				}
 
 				// Make sure we only write the first line to the output.
 				// This is needed if a description contains a linebreak.
 				// Otherwise the shell scripts will interpret the other lines as new flags
 				// and could therefore provide a wrong completion.
-				comp = strings.Split(comp, "\n")[0]
+				comp = strings.SplitN(comp, "\n", 2)[0]
 
 				// Finally trim the completion.  This is especially important to get rid
 				// of a trailing tab when there are no description following it.