fix the dets order issue

[LalehB]

This fixes the fallback logic for the geometric ordering (when no coordinates are present). originally we used emplace_back on a pre-sized vector and std::iota with incorrect iterators, resulting in the detector orders not being filled correctly.
this solves those errors with :

tesseract: src/tesseract.cc:106: TesseractDecoder::TesseractDecoder(TesseractConfig): Assertion `config.det_orders[i].size() == config.dem.count_detectors()' failed.

[noajshu]

Nice catch!