Use the current parser location for CSS error

… rather than the start location of the current construct.
This likely places the error just *after* of the unexpected token
whereas before would be best, but that’s likely a much bigger change.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1378861

components/style/stylesheets/stylesheet.rs

@@ -396,8 +396,9 @@ impl Stylesheet {
                     },
                     Err(err) => {
                         let error = ContextualParseError::InvalidRule(err.slice, err.error);
+                        let location = iter.input.current_source_location();
                         iter.parser.context.log_css_error(&iter.parser.error_context,
-                                                          err.location, error);
+                                                          location, error);
                     }
                 }
             }