fix: https://github.com/google/blockly/issues/161
fix: https://github.com/google/blockly/issues/161

On iOS, if I use a pinch gesture in the workspace, these errors appear in the console:

Error: Invalid value for <rect> attribute x="NaN"

google/blockly,3agv2004/Programming,sclements/scratch-blocks,InspectorWidget/blockly,nickmain/blockly,gengshenghong/scratch-blocks,mark-friedman/blockly,nickmain/blockly,eclecticdave/blockly,ocadotechnology/blockly,Andrews9008/blockly,rasata/blockly,eclecticdave/blockly,drigz/blockly,thr0w/blockly,toebes-extreme/blockly,aninternetof/blockly,mark-friedman/blockly,ralic/blockly,google/blockly,jisqyv/blockly,ocadotechnology/blockly,aravart/speech-blocks,markocelan/blockly-minecraft,aseba-community/blockly,mark-friedman/blockly,nickmain/blockly,nickmain/blockly,mark-friedman/blockly,picklesrus/blockly,dhalupa/blockly,UIKit0/blockly,daarond/blockly,andersschuller/blockly,eclecticdave/blockly,groklearning/blockly,sonwh98/blockly,lzairdking/blockly,Immortalin/blockly,trinketapp/blockly,CocoMake7/CocoBlockly,sclements/scratch-blocks,markocelan/blockly-minecraft,google/blockly-devtools,gudtago/blockly,picklesrus/blockly,toebes-extreme/blockly,rachel-fenichel/blockly,twodee/blockly,gengshenghong/scratch-blocks,ChinJY/blockly,stefan-j/blockly,daarond/blockly,sonwh98/blockly,shabesoglu/blockly,griffpatch/scratch-blocks,nickmain/blockly,carlosperate/blockly,ralic/blockly,kingoo/blockly,griffpatch/scratch-blocks,aninternetof/blockly,HALtheWise/blockly,picklesrus/blockly,cmillani/blockly,carlosperate/ardublockly,OpenRoberta/blockly,trinketapp/blockly,zerar/blockly,drigz/blockly,jano42/blockly,stefan-j/blockly,joshlory/blockly,jstnhuang/blockly,markocelan/blockly-minecraft,griffpatch/scratch-blocks,drigz/blockly,Immortalin/blockly,zerar/blockly,shabesoglu/blockly,marianoguerra/blockly,marianoguerra/blockly,twodee/blockly,google/blockly,jisqyv/blockly,groklearning/blockly,google/blockly,TechplexEngineer/blockly,touqir14/blockly,rachel-fenichel/blockly,google/blockly,hkoi/blockly,kingoo/blockly,aseba-community/blockly,jstnhuang/blockly,wakashige/blockly,michalkilawok/blockly,cmillani/blockly,ChinJY/blockly,marianoguerra/blockly,rasata/blockly,LLK/scratch-blocks,nickmain/blockly,gupta137/blockly,in1004kyu/tokitool,LLK/scratch-blocks,dhalupa/blockly,CocoMake7/CocoBlockly,edbutler/blockly,aninternetof/blockly,cmillani/blockly,altereagle/blockly,daarond/blockly,UIKit0/blockly,3agv2004/Programming,trodi/blockly,MaryS94/blockly,rachel-fenichel/blockly,jstnhuang/blockly,SheldonPacotti/blockly-enhancements,stefan-j/blockly,MaryS94/blockly,thr0w/blockly,altereagle/blockly,UIKit0/blockly,carlosperate/blockly,twodee/blockly,TechplexEngineer/blockly,ocadotechnology/blockly,OpenRoberta/blockly,gengshenghong/scratch-blocks,gengshenghong/scratch-blocks,RealTimeWeb/blockly,RealTimeWeb/blockly,carlosperate/ardublockly,kingoo/blockly,3agv2004/Programming,CocoMake7/CocoBlockly,aravart/speech-blocks,trodi/blockly,trinketapp/blockly,Gamefroot/Gamefroot-Blockly,wakashige/blockly,carloslfu/blockly,dhalupa/blockly,rachel-fenichel/blockly,twodee/blockly,sclements/scratch-blocks,jano42/blockly,trodi/blockly,sclements/scratch-blocks,lzairdking/blockly,toebes-extreme/blockly,rachel-fenichel/blockly,Tinkerforge/tvpl-blockly,carloslfu/blockly,Immortalin/blockly,touqir14/blockly,gengshenghong/scratch-blocks,LLK/scratch-blocks,Tinkerforge/tvpl-blockly,mark-friedman/blockly,vinay5jan/blocklyExtended,hybrideagle/blockly,HALtheWise/blockly,andersschuller/blockly,carlosperate/blockly,rasata/blockly,Gamefroot/Gamefroot-Blockly,gupta137/blockly,andersschuller/blockly,groklearning/blockly,hkoi/blockly,in1004kyu/tokitool,michalkilawok/blockly,SheldonPacotti/blockly-enhancements,LLK/scratch-blocks,twodee/blockly,gudtago/blockly,jano42/blockly,hybrideagle/blockly,LLK/scratch-blocks,Gamefroot/Gamefroot-Blockly,rachel-fenichel/blockly,wakashige/blockly,sonwh98/blockly,in1004kyu/tokitool,michalkilawok/blockly,carlosperate/ardublockly,mark-friedman/blockly,vinay5jan/blocklyExtended,zerar/blockly,griffpatch/scratch-blocks,griffpatch/scratch-blocks,SheldonPacotti/blockly-enhancements,OpenRoberta/blockly,gupta137/blockly,touqir14/blockly,lzairdking/blockly,google/blockly,rachel-fenichel/blockly,twodee/blockly,HALtheWise/blockly,trinketapp/blockly,jisqyv/blockly,ChinJY/blockly,edbutler/blockly,InspectorWidget/blockly,gudtago/blockly,hkoi/blockly,altereagle/blockly,Andrews9008/blockly,joshlory/blockly,aseba-community/blockly,carloslfu/blockly,vinay5jan/blocklyExtended,jstnhuang/blockly,lzairdking/blockly,carlosperate/blockly,stefan-j/blockly,google/blockly-devtools,OpenRoberta/blockly,joshlory/blockly,shabesoglu/blockly,RealTimeWeb/blockly,trodi/blockly,InspectorWidget/blockly,Tinkerforge/tvpl-blockly,thr0w/blockly,ralic/blockly,MaryS94/blockly,hybrideagle/blockly,edbutler/blockly,groklearning/blockly,markocelan/blockly-minecraft,sclements/scratch-blocks,Andrews9008/blockly,Gamefroot/Gamefroot-Blockly,google/blockly,jano42/blockly