Stop missing veg level from crashing the map js

Vendors missing veg levels will get coerced to 0. We are labeling
zero as "omni". We need to coerce to something because veg level is
an numeric data type and with the way templates fail silently, it is
occasionally empty.
Merge pull request #140 from steventlamb/bug/fix_map_js_veg_level

Stop missing veg level from crashing the map js