Sketcher: Augment malformed constraint messages

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

Enable a user recomputing an object/document to identify which sketch has the malformed constraints.

src/Mod/Sketcher/App/Sketch.cpp

@@ -69,6 +69,7 @@ Sketch::Sketch()
   , RecalculateInitialSolutionWhileMovingPoint(false)
   , GCSsys(), ConstraintsCounter(0)
   , isInitMove(false), isFine(true), moveStep(0)
+  , malformedConstraints(false)
   , defaultSolver(GCS::DogLeg)
   , defaultSolverRedundant(GCS::DogLeg)
   , debugMode(GCS::Minimal)
@@ -116,6 +117,7 @@ void Sketch::clear(void)
     isInitMove = false;
     ConstraintsCounter = 0;
     Conflicting.clear();
+    malformedConstraints = false;
 }
 
 int Sketch::setUpSketch(const std::vector<Part::Geometry *> &GeoList,
@@ -1493,6 +1495,7 @@ int Sketch::addConstraints(const std::vector<Constraint *> &ConstraintList)
 
         if(rtn == -1) {
             Base::Console().Error("Sketcher constraint number %d is malformed!\n",cid);
+            malformedConstraints = true;
         }
     }
 
@@ -1511,6 +1514,7 @@ int Sketch::addConstraints(const std::vector<Constraint *> &ConstraintList,
 
             if(rtn == -1) {
                 Base::Console().Error("Sketcher constraint number %d is malformed!\n",cid);
+                malformedConstraints = true;
             }
         }
         else {