Rhino has high CPU usage and potential DoS when passing specific numbers to `toFixed()` function

When an application passed an attacker controlled float poing number into the toFixed() function, it might lead to high CPU consumption and a potential Denial of Service.

Small numbers go through this call stack: NativeNumber.numTo > DToA.JS_dtostr > DToA.JS_dtoa > DToA.pow5mult where pow5mult attempts to raise 5 to a ridiculous power.

Example code: (4.47118444E-314).toFixed(2)