Merge pull request jupyter-xeus#140 from awvwgk/prompt-example

Out of range error in prompt example for ENTER input

Author: certik

examples/prompt.cpp

@@ -12,7 +12,7 @@ using Term::Terminal;
 bool determine_completeness([[maybe_unused]] std::string command) {
  // Determine if the statement is complete
  bool complete;
- if (command.substr(command.size() - 2, 1) == "\\") {
+ if (command.size() > 1 && command.substr(command.size() - 2, 1) == "\\") {
  complete = false;
  } else {
  complete = true;