If radix is outside Character.MIN_RADIX..Character.MAX_RADIX, this
method should throw IllegalArgumentException but
it either throws ArithmeticException (/ by zero) or returns 0

==== Here is the minimized test demonstrating the bug ====
import java.lang.Bignum;
class java_lang_Bignum_createFromRadixString {
  public static void main(String args[]) {
    Bignum b1=Bignum.createFromRadixString("1",40);
    System.out.println(b1);
    Bignum b2=Bignum.createFromRadixString("1",1);
    System.out.println(b2);
  }
}
==== Here is the output of the test ====
0
java.lang.ArithmeticException: / by zero
at java.lang.Bignum.createFromRadixString(Bignum.java)
at java_lang_Bignum_createFromRadixString.main(java_lang_Bignum_createFromRadixString.java:6)