It's possible to get NaN and other Misc issues with NaN

[AustinTSchaffer]

It appears that the stack does not default to 0 if you repeat operators.

Steps to reproduce:

1. Refresh
2. Repeat any operator until NaN appears in the calc window.

Other issues with NaN

• You can store NaN on the stack with the Up button or the "Return" key.
• You can delete "digits" of NaN with backspace, which can be stored on the stack
• You can add "digits" to NaN, Na, or N using the other number keys, which can also be stored on the stack.
• Starting from a refresh, you can generate an infinite stack of NaNs using the input sequence
  • divide
  • up
  • up
• Starting from a refresh, you can generate a Batman sequence using the input sequence
  • divide
  • back
  • up
  • up