helpers: add isDigitWord() function

returns true if all chars of string parameter are digits


Origin commit data
------------------
Commit: 205bbeb7ce
Author: Thilo Graf <dbt@novatux.de>
Date: 2019-03-28 (Thu, 28 Mar 2019)

src/system/helpers.cpp

@@ -1929,4 +1929,13 @@ std::string encodeUrl(std::string txt)
 	return txt;
 }
 
+bool isDigitWord(std::string str)
+{
+	for (size_t i=0; i < str.size(); i++)
+		if (!isdigit(str[i]))
+			return false;
+
+	return true;
+}
+
 //