rml2pdf: better message if a font is not available.

Since 91422704d965268f, specifying a font that is not registered with
pdfmetrics will raise an exception. Now, improve that exception to
help the user understand what has gone wrong.

Note: rather than hiding the fact that some font is missing, the admin
should see this error and try to either fix the report (to use a known
font), or register more fonts with the customfonts.py mechanism.

bzr revid: p_christ@hol.gr-20101123153235-c1yri33ptaydb5eo

bin/report/render/rml2pdf/trml2pdf.py

@@ -486,7 +486,10 @@ class _rml_canvas(object):
 
     def setFont(self, node):
         fname = node.get('name')
-        return self.canvas.setFont(fname, utils.unit_get(node.get('size')))
+        try:
+            return self.canvas.setFont(fname, utils.unit_get(node.get('size')))
+        except KeyError, e:
+            raise KeyError('Font "%s" is not registered in the engine' % fname)
 
     def render(self, node):
         tags = {