don't crash on bad input data

Post/PViewDataGModel.h

@@ -114,6 +114,7 @@ class stepData{
   }
   Real *getData(int index, bool allocIfNeeded=false, int mult=1)
   {
+    if(index < 0) return 0;
     if(allocIfNeeded){
       if(index >= getNumData()) resizeData(index + 100); // optimize this
       if(!(*_data)[index]){

Post/PViewDataGModelIO.cpp

@@ -89,6 +89,7 @@ bool PViewDataGModel::readMSH(const std::string &viewName, const std::string &fi
     else{
       if(fscanf(fp, "%d", &num) != 1) return false;
     }
+    if(num < 0) return false;
     int mult = 1;
     if(_type == ElementNodeData || _type == GaussPointData){
       if(binary){