Codechange: Use EncodedString for error messages. (#13569)

src/strings_func.h

@@ -138,6 +138,18 @@ std::string GetString(StringID string, Args &&... args)
 EncodedString GetEncodedString(StringID str);
 EncodedString GetEncodedStringWithArgs(StringID str, std::span<const StringParameter> params);
 
+/**
+ * Encode a string with no parameters into an encoded string, if the string id is valid.
+ * @note the return encoded string will be empty if the string id is not valid.
+ * @param str String to encode.
+ * @returns an EncodedString.
+ */
+static inline EncodedString GetEncodedStringIfValid(StringID str)
+{
+	if (str == INVALID_STRING_ID) return {};
+	return GetEncodedString(str);
+}
+
 /**
  * Get an encoded string with parameters.
  * @param string String ID to encode.