fix case in which file is created and backup is requested but fails, not it just doesn't attempt to backup the missing file

Signed-off-by: Brian Coca <briancoca+ansible@gmail.com>

lineinfile

@@ -143,7 +143,7 @@ def present(module, dest, regexp, line, insertafter, create, backup):
         changed = True
 
     if changed:
-        if backup:
+        if backup and os.path.exists(dest):
             module.backup_local(dest)
         f = open(dest, 'wb')
         f.writelines(lines)