[Clp] Clp_addRows causes incorrect solution for zero coefficient

[coinor at henning-thielemann.de]

I have written a Haskell binding to COIN-OR/Clp and added a test-suite 
with automated QuickCheck tests. It spot the following problem:
   https://hydra.nixos.org/build/239790474/nixlog/2

I think this is a bug in Clp_addRows. I have simplified the problem and 
extracted a minimal example using the C interface, see attached code.

It is a super simple problem consisting of one variable and one equation.

With the 'if' clause you can switch between Clp_addRows and 
Clp_loadProblem.

Clp_addRows yields

$ a.out
Clp0024I Matrix will be packed to eliminate 1 small elements
Clp0000I Optimal - objective value 0

which is wrong.


Clp_loadProblem yields

$ a.out
Clp3002W Empty problem - 1 rows, 1 columns and 0 elements
Clp0000I Optimal - objective value 84

which is right.


Clp_addRows works correctly, when the coefficient is not zero or when I 
specify no term for the row, at all.
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