Fix Divide By Zero Error if No Votes

Fix divide by zero error if no votes in survey.

Possible future addition would be validation to prevent submitting form
if not votes.
Remove `$value=0` From Previous Commit

Previous commit incorrectly set `$value=0` and caused issue with graph
rendering
Merge pull request #970 from mkly/fix_survey_block_divide_by_zero

Fix Divide By Zero Error if No Votes