don't be that strict regarding illegal characters in `mp_read_radix()`

bn_mp_read_radix.c

@@ -73,7 +73,7 @@ int mp_read_radix (mp_int * a, const char *str, int radix)
   }
 
   /* if an illegal character was found, fail. */
-  if (*str != '\0') {
+  if (!(*str == '\0' || *str == '\r' || *str == '\n')) {
       mp_zero(a);
       return MP_VAL;
   }