Remove the whole ring / linestring if number of vertices to small

src/core/geometry/qgscurvepolygonv2.cpp

@@ -702,7 +702,7 @@ bool QgsCurvePolygonV2::deleteVertex( const QgsVertexId& vId )
 
   QgsCurveV2* ring = vId.ring == 0 ? mExteriorRing : mInteriorRings.at( vId.ring - 1 );
   int n = ring->numPoints();
-  if ( n <= 2 )
+  if ( n <= 4 )
   {
     //no points will be left in ring, so remove whole ring
     if ( vId.ring == 0 )

src/core/geometry/qgslinestringv2.cpp

@@ -644,6 +644,12 @@ bool QgsLineStringV2::deleteVertex( const QgsVertexId& position )
   {
     mM.remove( position.vertex );
   }
+
+  if( numPoints() == 1 )
+  {
+    clear();
+  }
+
   mBoundingBox = QgsRectangle(); //set bounding box invalid
   return true;
 }