fix crash due to non-check of return value of FOpen in BackgroundField::print().

Sigh...

Mesh/BackgroundMesh.cpp

@@ -177,7 +177,6 @@ static void propagateValuesOnFace(GFace *_gf,
     myAssembler.fixVertex(itv->first, 0, 1, itv->second);
   }
 
-
   // Number vertices
   std::set<MVertex*> vs;
   for (unsigned int k = 0; k < _gf->triangles.size(); k++)
@@ -348,7 +347,8 @@ void backgroundMesh::propagateCrossFieldByDistance(GFace *_gf)
 #endif
 }
 
-inline double myAngle (const SVector3 &a, const SVector3 &b, const SVector3 &d){
+inline double myAngle (const SVector3 &a, const SVector3 &b, const SVector3 &d)
+{
   double cosTheta = dot(a,b);
   double sinTheta = dot(crossprod(a,b),d);
   return atan2 (sinTheta,cosTheta);
@@ -403,7 +403,6 @@ double backgroundMesh::getSmoothness(double u, double v, double w)
 
 void backgroundMesh::propagateCrossField(GFace *_gf)
 {
-  //  printf("coucou\n");
   propagateCrossFieldHJ (_gf);
   // solve the non liear problem
   constantPerElement<double> C;
@@ -424,13 +423,13 @@ void backgroundMesh::propagateCrossField(GFace *_gf)
     if (++ITER > 0)break;
   }
   //  printf("converged in %d iterations\n", ITER);
+#if 0 // debug print
   char name[256];
   sprintf(name, "cross-%d-%d.pos", _gf->tag(), ITER);
   print(name, 0, 1);
   sprintf(name, "smooth-%d-%d.pos", _gf->tag(), ITER);
   print(name, _gf, 2);
-
-
+#endif
 }
 
 void backgroundMesh::propagateCrossFieldHJ(GFace *_gf)
@@ -650,6 +649,10 @@ void backgroundMesh::print(const std::string &filename, GFace *gf,
                            const std::map<MVertex*,double> &_whatToPrint, int smooth)
 {
   FILE *f = Fopen (filename.c_str(),"w");
+  if(!f){
+    Msg::Warning("Could not open file '%s'", filename.c_str());
+    return;
+  }
   fprintf(f, "View \"Background Mesh\"{\n");
   if (smooth){
     for(unsigned int i = 0; i < gf->triangles.size(); i++){
@@ -693,6 +696,7 @@ void backgroundMesh::print(const std::string &filename, GFace *gf,
 }
 
 MElementOctree* backgroundMesh::get_octree(){
+
   return _octree;
 }