Sketcher: Bug fix: Unexpected crashes during certain operations
Sketcher: Bug fix: Unexpected crashes during certain operations

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

The sketcher crashed for example during effecting a fillet operation.

Cause:
The ElementsWidget/ConstraintWidget was being updated as a consequence of adding/removing geometry/constraints, and it was effecting
a selection after the update, in cases where the geometry in the screen was not being redraw (because the sketchobject was still unsolved), therefore
trying to select an element that according to ViewProvider did not exist (as it is created during redraw).

Solution:
Widgets update when their properties changes, provided that a redraw is effected (which actually also saves some (negligible) time, as they are only updated when they should).

Creworker/FreeCAD,usakhelo/FreeCAD,Creworker/FreeCAD,chrisjaquet/FreeCAD,jriegel/FreeCAD,usakhelo/FreeCAD,timthelion/FreeCAD,wood-galaxy/FreeCAD,wood-galaxy/FreeCAD,yantrabuddhi/FreeCAD,wood-galaxy/FreeCAD,timthelion/FreeCAD,kkoksvik/FreeCAD,YuanYouYuan/FreeCAD,jriegel/FreeCAD,bblacey/FreeCAD-MacOS-CI,elgambitero/FreeCAD_sf_master,dsbrown/FreeCAD,dsbrown/FreeCAD,usakhelo/FreeCAD,Fat-Zer/FreeCAD_sf_master,marcoitur/FreeCAD,cypsun/FreeCAD,timthelion/FreeCAD,thdtjsdn/FreeCAD,marcoitur/Freecad_test,elgambitero/FreeCAD_sf_master,maurerpe/FreeCAD,usakhelo/FreeCAD,mickele77/FreeCAD,wood-galaxy/FreeCAD,bblacey/FreeCAD-MacOS-CI,Fat-Zer/FreeCAD_sf_master,Creworker/FreeCAD,bblacey/FreeCAD-MacOS-CI,jonnor/FreeCAD,maurerpe/FreeCAD,mickele77/FreeCAD,elgambitero/FreeCAD_sf_master,marcoitur/FreeCAD,mickele77/FreeCAD,cpollard1001/FreeCAD_sf_master,cypsun/FreeCAD,Fat-Zer/FreeCAD_sf_master,Alpistinho/FreeCAD,chrisjaquet/FreeCAD,dsbrown/FreeCAD,bblacey/FreeCAD-MacOS-CI,chrisjaquet/FreeCAD,mickele77/FreeCAD,yantrabuddhi/FreeCAD,cypsun/FreeCAD,YuanYouYuan/FreeCAD,marcoitur/Freecad_test,timthelion/FreeCAD,jriegel/FreeCAD,yantrabuddhi/FreeCAD,bblacey/FreeCAD-MacOS-CI,chrisjaquet/FreeCAD,cypsun/FreeCAD,marcoitur/Freecad_test,yantrabuddhi/FreeCAD,chrisjaquet/FreeCAD,usakhelo/FreeCAD,thdtjsdn/FreeCAD,marcoitur/Freecad_test,Creworker/FreeCAD,usakhelo/FreeCAD,jonnor/FreeCAD,Alpistinho/FreeCAD,mickele77/FreeCAD,timthelion/FreeCAD,jriegel/FreeCAD,Alpistinho/FreeCAD,cpollard1001/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,chrisjaquet/FreeCAD,jriegel/FreeCAD,thdtjsdn/FreeCAD,maurerpe/FreeCAD,Alpistinho/FreeCAD,maurerpe/FreeCAD,dsbrown/FreeCAD,thdtjsdn/FreeCAD,YuanYouYuan/FreeCAD,chrisjaquet/FreeCAD,cpollard1001/FreeCAD_sf_master,usakhelo/FreeCAD,marcoitur/Freecad_test,wood-galaxy/FreeCAD,marcoitur/FreeCAD,wood-galaxy/FreeCAD,kkoksvik/FreeCAD,Fat-Zer/FreeCAD_sf_master,cypsun/FreeCAD,jonnor/FreeCAD,elgambitero/FreeCAD_sf_master,maurerpe/FreeCAD,YuanYouYuan/FreeCAD,jonnor/FreeCAD,Alpistinho/FreeCAD,timthelion/FreeCAD,cpollard1001/FreeCAD_sf_master,YuanYouYuan/FreeCAD,marcoitur/FreeCAD,Creworker/FreeCAD,cpollard1001/FreeCAD_sf_master,elgambitero/FreeCAD_sf_master,dsbrown/FreeCAD,kkoksvik/FreeCAD,marcoitur/FreeCAD,kkoksvik/FreeCAD,bblacey/FreeCAD-MacOS-CI,jonnor/FreeCAD,bblacey/FreeCAD-MacOS-CI,kkoksvik/FreeCAD,yantrabuddhi/FreeCAD,thdtjsdn/FreeCAD