fix: cgitb crashes if there is no line number set.

I am not sure why:

  context.position[0]

is None when an exception happens while processing templates. This
causes a second exception because of a print statement matching %d to
None.  The second exception blows away any chance at getting useful
info.  So fix it by passing line number -1. Hopefully people will
recognize that as bogus and interpret it as no line number was
available.

Fixing the underlying cause (in ZopeTAL???) would be better though.

CHANGES.txt

@@ -100,6 +100,11 @@ Fixed:
   request.client.additional_headers) to application/json and return
   json from the template. This json could access the 1i18n functions
   for a javascript helper. (John Rouillard)
+- when template processing raises an exception the line number is
+  sometimes missing. This causes cgitb to raise a second exception
+  which clobbers the info about the template issue. As a stop-gap set
+  the line number to -1 so the original traceback can be seen. This
+  could be a bug in ZopeTAL. (John Rouillard)
 
 Features:
 

roundup/cgi/cgitb.py

@@ -104,7 +104,7 @@ def pt_html(context=5, i18n=None):
 </table></li>
 ''') % {
     'info': info,
-    'line': context.position[0],
+    'line': context.position[0] or -1,
     'globals': niceDict('    ', context.global_vars),
     'locals': niceDict('    ', context.local_vars)
    })