When shifting a negative BigInt value if the
shift count is very "big" the result should be -1.
eg.:
```
(-2n >> (2n*32n)) === -1n
```
Note: the `-2n >> (2n*31n)` already returned `-1n` prior this change.
JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.usz@partner.samsung.com
Péter Gál