Multiline edge labels throw an exception #2386

`labelLineHeight` must be prefixed like other label values, because of source and target labels.  Using multiline labels for source and target sides of an edge doesn't generally make sense, but this change is necessary for the value for the main edge label to be distinct from the others.  This issue is caused by the addition of the line-height style property #2115.

src/extensions/renderer/base/coord-ele-math/labels.js

@@ -301,7 +301,8 @@ BRp.applyPrefixedLabelDimensions = function( ele, prefix ){
   let labelDims = this.calculateLabelDimensions( ele, text );
   let lineHeight = ele.pstyle('line-height').pfValue;
   let textWrap = ele.pstyle('text-wrap').strValue;
-  let numLines = textWrap !== 'wrap' ? 1 : (util.getPrefixedProperty( _p.rscratch, 'labelWrapCachedLines', prefix ).length || 1);
+  let lines = util.getPrefixedProperty( _p.rscratch, 'labelWrapCachedLines', prefix ) || [];
+  let numLines = textWrap !== 'wrap' ? 1 : Math.max(lines.length, 1);
   let normPerLineHeight = labelDims.height / numLines;
   let labelLineHeight = normPerLineHeight * lineHeight;
 
@@ -314,7 +315,7 @@ BRp.applyPrefixedLabelDimensions = function( ele, prefix ){
   util.setPrefixedProperty( _p.rstyle,   'labelHeight', prefix, height );
   util.setPrefixedProperty( _p.rscratch, 'labelHeight', prefix, height );
 
-  _p.rscratch.labelLineHeight = labelLineHeight;
+  util.setPrefixedProperty( _p.rscratch, 'labelLineHeight', prefix, labelLineHeight );
 };
 
 BRp.getLabelText = function( ele, prefix ){

src/extensions/renderer/canvas/drawing-label-text.js

@@ -319,7 +319,7 @@ CRp.drawText = function( context, ele, prefix, applyRotation = true, useEleOpaci
 
     if( ele.pstyle( 'text-wrap' ).value === 'wrap' ){
       let lines = util.getPrefixedProperty( rscratch, 'labelWrapCachedLines', prefix );
-      let lineHeight = _p.rscratch.labelLineHeight;
+      let lineHeight = util.getPrefixedProperty( rscratch, 'labelLineHeight', prefix );
       let halfTextW = textW/2;
       let justification = this.getLabelJustification(ele);