Change auto diff jacobian storage order when vertex dimension is 1

[otamachan]

Hi,
When I use audo diff with a one dimension vertex, Eigen generates a static assert and compilation fails.
It seems that Eigen does now allow Eigen::RowMajor if the column size is 1.
This patch changes the jacobian storage order if the vertex dimension is 1 to avoid this error.

Here is a reproducable example

#include <g2o/core/auto_differentiation.h>
#include <g2o/core/base_unary_edge.h>
#include <g2o/types/slam2d/vertex_se2.h>

#include <Eigen/Core>
#include <vector>

class VertexTest : public g2o::BaseVertex<1, double> {};

class EdgeTest
    : public g2o::BaseUnaryEdge<2, Eigen::Vector2d, VertexTest> {
 public:
  EIGEN_MAKE_ALIGNED_OPERATOR_NEW
  EdgeTest() {}
  template <typename T>
  bool operator()(const T *v, T *error) const {
    return true;
  }

  G2O_MAKE_AUTO_AD_FUNCTIONS_BY_GET
  bool read(std::istream &) override { return true; }
  bool write(std::ostream &os) const override { return os.good(); }
};

int main() {
}

/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h: In instantiation of 'static void Eigen::PlainObjectBase<Derived>::_check_template_params() [with Derived = Eigen::Matrix<double, 2, 1, 1, 2, 1>]':
/usr/include/eigen3/Eigen/src/Core/Matrix.h:261:35:   required from 'Eigen::Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::Matrix() [with _Scalar = double; int _Rows = 2; int _Cols = 1; int _Options = 1; int _MaxRows = 2; int _MaxCols = 1]'
/usr/include/c++/9/tuple:123:22:   required from 'constexpr std::_Head_base<_Idx, _Head, false>::_Head_base() [with long unsigned int _Idx = 0; _Head = Eigen::Matrix<double, 2, 1, 1, 2, 1>]'
/usr/include/c++/9/tuple:340:15:   required from 'static void g2o::AutoDifferentiation<Edge, EstimateAccess>::linearizeOplusNs(Edge*, std::index_sequence<Ints ...>) [with long unsigned int ...Ints = {0}; Edge = EdgeTest; EstimateAccess = g2o::EstimateAccessorGet<EdgeTest>; std::index_sequence<Ints ...> = std::integer_sequence<long unsigned int, 0>]'
third_party/g2o/g2o/core/auto_differentiation.h:180:21:   required from 'static void g2o::AutoDifferentiation<Edge, EstimateAccess>::linearize(Edge*) [with Edge = EdgeTest; EstimateAccess = g2o::EstimateAccessorGet<EdgeTest>]'
test.cpp:20:3:   required from here
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:903:7: error: static assertion failed: INVALID_MATRIX_TEMPLATE_PARAMETERS
  903 |       EIGEN_STATIC_ASSERT((EIGEN_IMPLIES(MaxRowsAtCompileTime==1 && MaxColsAtCompileTime!=1, (Options&RowMajor)==RowMajor)
      |       ^~~~~~~~~~~~~~~~~~~
make[2]: *** [CMakeFiles/test.dir/build.make:63: CMakeFiles/test.dir/src/test.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:1222: CMakeFiles/test.dir/all] Error 2
make: *** [Makefile:152: all] Error 2

[codecov]

Codecov Report

Merging #725 (8b94ea9) into master (babd2c7) will not change coverage.
Report is 3 commits behind head on master.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #725   +/-   ##
=======================================
  Coverage   50.96%   50.96%           
=======================================
  Files         271      271           
  Lines       10986    10986           
=======================================
  Hits         5599     5599           
  Misses       5387     5387           

Files	Coverage Δ
g2o/core/auto_differentiation.h	78.94% <ø> (ø)

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