Bogus enum constant explicit promotion when previous value was negative

[PathogenDavid]

Found in ImPlot:

https://github.com/epezent/implot/blob/fc0fd112467c2be84bc56daa57612b0c579ff1af/implot.h#L406-L420

ImPlotMarker_Circle will be emitted with an explicit value and result in a bogus warning:

Warning: ImPlotMarker.Circle had an implicit value, but it had to be translated with an explicit one.

However, emitting this as it was written in C++ is plenty fine in C#.