Reassign feature flaw

Should not allow user to assign values that are below 0

![image.png](https://raw.githubusercontent.com/CheeSengg/ped/master/files/1531e17c-19da-4dbf-8513-30673f32db49.png)


![image.png](https://raw.githubusercontent.com/CheeSengg/ped/master/files/067d63a3-e86e-4ea2-a4cf-a7b7cf0afeca.png)



