Fix JSON issue where remaining hours is reset when attribute is not in params array.

See http://forum.redminebacklogs.net/quot-Remaining-hours-quot-field-deleted-upon-JSON-ticket-update-td4025855.html

Author: bohansen

lib/backlogs_hooks.rb

@@ -343,7 +343,7 @@ def controller_issues_edit_before_save(context={ })
         params = context[:params]
         issue = context[:issue]
 
-        if issue.is_task?
+        if issue.is_task? && params.include?(:remaining_hours)
           begin
             issue.remaining_hours = Float(params[:remaining_hours])
           rescue ArgumentError, TypeError