apk: properly error out if an unknown command is requested

src/apk.c

@@ -579,6 +579,10 @@ int main(int argc, char **argv)
 	}
 
 	if (applet == NULL) {
+		if (argc > 1) {
+			r = 1;
+			apk_error("'%s' is not an apk command. See 'apk --help'.", argv[1]);
+		} else
 			r = usage(NULL);
 		goto err;
 	}