Number overflow in the transaction deadline input

[R1nlz3r]

Description :
Hello, I tried to put random stuff into the "Transaction deadline" input to see if it breaks.
If you enter a too big number it overflows, throws an error, breaks the client side (blank screen) and stays in the cookie.
You have to delete your cookie to recover a normal state.
Putting some conditions in place to check if the input value is valid before processing it could solve the issue.

Path to input :
Transactions settings > Transactions deadline.

Steps to reproduce :
Copy / paste "999999999999999999" into the input.

[bmino]

Good find! Would you be able / willing to submit a PR to address this?