throw exception if string is not selected length

lib/secure-random-string.js

@@ -31,6 +31,9 @@ function srs(options, cb) {
 		} else {
 			string = string.replace(/\//g, '_').replace(/\+/g, '-');
 		}
+		if (string.length < length) {
+			throw new Error(`Generated string is too short. Please catch this Error and try again.`);
+		}
 		return string.substr(0, length);
 	}
 };