Block custom, visibility, and pages properties need to be checked for existence before they are used.

After recently installing OM Maximenu, we started noticing these error messages showing up on some pages:

Notice: Undefined property: stdClass::$custom in om_maximenu_blocks_visibility() (line 382 of /home/newad/public_html/sites/all/modules/om_maximenu/inc/om_maximenu.render.inc).
Notice: Undefined property: stdClass::$visibility in om_maximenu_blocks_visibility() (line 395 of /home/newad/public_html/sites/all/modules/om_maximenu/inc/om_maximenu.render.inc).
Notice: Undefined property: stdClass::$pages in om_maximenu_blocks_visibility() (line 405 of /home/newad/public_html/sites/all/modules/om_maximenu/inc/om_maximenu.render.inc).

After some digging, it was determined this was an interaction between OM Maximenu and Node Level Blocks. Evidently, if a block in placed in a node via Node Level Blocks, the custom, visibility, and pages properties end up missing for that block in the block list. The code needs to check if these properties exist before using them.