RFR 8174797: jshell tool: invalid module path crashes tool

[Robert Field]

Please review (ASAP)....

Bugs:

     8174797: jshell tool: invalid module path crashes tool
     https://bugs.openjdk.java.net/browse/JDK-8174797

     8174796: jshell tool: regression: user home (tilde) not translated
     https://bugs.openjdk.java.net/browse/JDK-8174796

Webrev:

     http://cr.openjdk.java.net/~rfield/8174797v0.webrev/

Thanks,
Robert