ion_decimal_from_ion_int Returns NaN

[almann]

When implementing ion-c-sys in Rust, I ran into amzn/ion-rust/issues/#79. Specifically, this API appears to return nan for at least the following ION_INT values:

57516904150035820771702738217456585
77008733801862767698341856677462573
4623874712756984956766514373293465450
9970304500552494301196940956407522192
59025723530133359201873978774331457987
19141033431585215614236049655094977149
44818084368071883463971983799827359329516552715395136426901699171061657459862827
11050923646496935500303958597719760541602476378798913802309108901778807590265278
429926815238794553771012929776377470059985366468509955296419658127318674237363065734779169
72528362571947544011741381371920928164665526193613163529470013995124245887784236337589645597617

When tracing this in the debugger, the decContext is set to DEC_Invalid_context, but the routine returns iERR_OK.