Show a better error message if Java is not configured.

vasl_templates/webapp/main.py

@@ -235,9 +235,13 @@ def get_program_info():
         return tstamp + timedelta( minutes=tz_offset )
 
     # set the basic details
+    try:
+        vassal_version = VassalShim.get_version()
+    except Exception: #pylint: disable=broad-except
+        vassal_version = "???"
     params = {
         "APP_VERSION": vasl_templates.webapp.config.constants.APP_VERSION,
-        "VASSAL_VERSION": VassalShim.get_version()
+        "VASSAL_VERSION": vassal_version
     }
     build_git_info = get_build_git_info()
     if build_git_info:

vasl_templates/webapp/vassal.py

@@ -435,6 +435,8 @@ class VassalShim:
             if compare_version_strings( mo.group(), "3.3.0" ) < 0:
                 # we're using a legacy version of VASSAL - use Java 8
                 java_path = java8_path
+        if not java_path:
+            raise SimpleError( "Java has not been configured." )
 
         # prepare the command
         class_path = app.config.get( "JAVA_CLASS_PATH" )