Sketcher: PropertyConstraintList input data validation

======================================================

PropertyConstraintList is provided with the ability to check its constraints indices against
a minimum and a maximum, and set an invalidindex status.

In this status, the getValues returns an emptylist, as in the case with invalid geometry types.

src/Mod/Sketcher/App/PropertyConstraintList.cpp

@@ -61,6 +61,7 @@ PropertyConstraintList::PropertyConstraintList()
   : validGeometryKeys(0)
   , invalidGeometry(true)
   , restoreFromTransaction(false)
+  , invalidIndices(false)
 {
 
 }
@@ -400,6 +401,41 @@ bool PropertyConstraintList::checkGeometry(const std::vector<Part::Geometry *> &
     return invalidGeometry;
 }
 
+bool PropertyConstraintList::checkConstraintIndices(int geomax, int geomin)
+{
+    int mininternalgeoid = std::numeric_limits<int>::max();
+    int maxinternalgeoid = Constraint::GeoUndef;
+
+    auto cmin = [] (int previousmin, int cindex) {
+        if( cindex == Constraint::GeoUndef )
+            return previousmin;
+
+        return ( cindex < previousmin )? cindex : previousmin;
+    };
+
+    auto cmax = [] (int previousmax, int cindex) {
+        return ( cindex > previousmax )? cindex : previousmax;
+    };
+
+    for (const auto &v : _lValueList) {
+
+        mininternalgeoid = cmin(mininternalgeoid, v->First);
+        mininternalgeoid = cmin(mininternalgeoid, v->Second);
+        mininternalgeoid = cmin(mininternalgeoid, v->Third);
+
+        maxinternalgeoid = cmax(maxinternalgeoid, v->First);
+        maxinternalgeoid = cmax(maxinternalgeoid, v->Second);
+        maxinternalgeoid = cmax(maxinternalgeoid, v->Third);
+    }
+
+    if(maxinternalgeoid > geomax || mininternalgeoid < geomin)
+        invalidIndices = true;
+    else
+        invalidIndices = false;
+
+    return invalidIndices;
+}
+
 /*!
  * \brief PropertyConstraintList::scanGeometry tests if the supplied geometry
  *  is the same (all elements are of the same type as they used to be).

src/Mod/Sketcher/App/PropertyConstraintList.h

@@ -99,11 +99,11 @@ public:
            returns null. This must be checked by the caller.
     */
     const Constraint *operator[] (const int idx) const {
-        return invalidGeometry ? 0 : _lValueList[idx];
+        return (invalidGeometry || invalidIndices) ? 0 : _lValueList[idx];
     }
 
     const std::vector<Constraint*> &getValues(void) const {
-        return invalidGeometry ? _emptyValueList : _lValueList;
+        return (invalidGeometry || invalidIndices) ? _emptyValueList : _lValueList;
     }
     const std::vector<Constraint*> &getValuesForce(void) const {//to suppress check for invalid geometry, to be used for sketch repairing.
         return  _lValueList;
@@ -124,6 +124,8 @@ public:
     bool checkGeometry(const std::vector<Part::Geometry *> &GeoList);
     bool scanGeometry(const std::vector<Part::Geometry *> &GeoList) const;
 
+    bool checkConstraintIndices(int geomax, int geomin);
+
     /// Return status of geometry for better error reporting
     bool hasInvalidGeometry() const { return invalidGeometry; }
 
@@ -162,6 +164,7 @@ private:
     std::vector<unsigned int> validGeometryKeys;
     bool invalidGeometry;
     bool restoreFromTransaction;
+    bool invalidIndices;
 
     void applyValues(std::vector<Constraint*>&&);
     void applyValidGeometryKeys(const std::vector<unsigned int> &keys);