Fix convexity unary

[svigerske]

On GAMS modellib model hda, I got a problem because std::dynamic_pointer_cast<ExpressionUnary>(child) was NULL even though child->getNumberOfChildren() == 1. Apparently, child was a product with only 1 child.

This pull request fixes this by checking that the expression is of type ExpressionUnary instead of checking the number of children.

[svigerske]

I don't know how to check why some tests failed. There is too little output to see whether that is connected to this pull-request.

[andreaslundell]

I will check this later. You can get more output from the tests with

test/test_runner <test> <number>

Where <test> is one of Model, Settings, Cbc, Cplex, Gurobi, GAMS, Solver or Ipopt. <number> is the test number that failed.

[svigerske]

The tests fail with

Starting test to solve problem with semicont. variables:
 Problem file "data/meanvarxsc.osil" does not exist.
Finished test to solve problem with semicont. variables.

I'll conclude that this has nothing to do with the changes in this pull request. You can probably easily add this file.