Describe the bug
When creating a numeric gradeable and uploading data to it as a CSV, gradeable component data of value 0 gets added to the database, when normally marking a component in a numeric gradeable with a value of 0 removes it from the database. These 0-value component data make it more difficult to delete columns that have had data uploaded from a CSV, as any column with data in it cannot be deleted, even these 0-value component data which do not normally occur when manually grading.

Expected behavior
If a CSV is uploaded to a numeric gradeable, any cells with value 0 should not be added as gradeable component data to the database.

To Reproduce
Steps to reproduce the behavior:

1. Log in as instructor
2. Create a new numeric gradeable with at least 2 numeric rows
3. Upload a CSV to fill in the table, with at least one cell of the CSV being a 0
4. Go to SQL-Toolbox and use the following db query: select * from gradeable_data join gradeable_component_data on gradeable_data.gd_id=gradeable_component_data.gd_id where g_id='<THE ID OF YOUR GRADEABLE>'
5. You will see entries with gcd_score = 0 wherever in your gradeable that the CSV uploaded a numeric value of 0. This is a bug; entries whose gcd_score is set to 0 should be removed from the database, to represent that that cell in the gradeable has no data and can be deleted.

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