Your taxable income on 1040 line 11b can not be less than zero so I don't know where you are seeing the negative amounts. And your Standard Deduction can be less than the 12,200.
The Standard Deduction for an individual for whom an exemption can be claimed on another person's tax return is limited to the greater of:
…..$1,100 or
…..Your earned income for the year + $350 (up to the max of 12,200)
So you would get a minimum of $1,100 up to the max of 12,200.
So by claiming yourself your SD might have increased up to the full 12,200 thereby reducing your taxable income (but not to less than zero).
