check for workspace command name arg

* check for workspace command name arg (fix #5131)

For the 'workspace <name> output <output>' command, output_location must
be greater than zero or the attempt to get the workspace name with
join_args will segfault or abort() (depending on the flavor of
sway_assert() in use). This checks and returns an error instead.

* put workspace output error string on one line

To ease grepping as requested

* check for name in workspace gaps command as well

A malformed command here will lead to the same result seen in #5131, so
add a check. Done inside the cmd_workspace_gaps() function itself, to
take advantage of the existing 'Expected...' string.

sway/commands/workspace.c

@@ -60,6 +60,9 @@ static struct cmd_results *cmd_workspace_gaps(int argc, char **argv,
 		int gaps_location) {
 	const char expected[] = "Expected 'workspace <name> gaps "
 		"inner|outer|horizontal|vertical|top|right|bottom|left <px>'";
+	if (gaps_location == 0) {
+		return cmd_results_new(CMD_INVALID, expected);
+	}
 	struct cmd_results *error = NULL;
 	if ((error = checkarg(argc, "workspace", EXPECTED_EQUAL_TO,
 					gaps_location + 3))) {
@@ -140,7 +143,10 @@ struct cmd_results *cmd_workspace(int argc, char **argv) {
 			break;
 		}
 	}
-	if (output_location >= 0) {
+	if (output_location == 0) {
+		return cmd_results_new(CMD_INVALID,
+			"Expected 'workspace <name> output <output>'");
+	} else if (output_location > 0) {
 		if ((error = checkarg(argc, "workspace", EXPECTED_AT_LEAST,
 						output_location + 2))) {
 			return error;