ECL problem: write the initial solution again

this regressed after time step index of the initial solution was
changed from 0 (actually, this was also 0 for the first time step...)
to -1 in b30af664.

tests/problems/eclproblem.hh

@@ -312,7 +312,7 @@ public:
      */
     bool shouldWriteOutput()
     {
-        if (this->simulator().timeStepIndex() == 0)
+        if (this->simulator().timeStepIndex() < 0)
             // always write the initial solution
             return true;