fix(Clefs): fix mid-measure clef added at wrong position (#954) because of forward/backup node.

fix #954 (together with 8b1d898750b524d2141eddcbe236173cc8705a16)

for now we don't add those clefs at all, because we would need to rework that
clefs are currently always saved for the currentStaffEntry.

actually using forward and backup nodes to position clefs (or for anything else)
is extremely bad MusicXML style,
and only seems to happen (for clefs) when exported by bad programs.

visual regression tests pass.

src/MusicalScore/ScoreIO/InstrumentReader.ts

@@ -141,8 +141,12 @@ export class InstrumentReader {
             currentMeasure.MeasureNumberXML = measureNumberXml;
         }
       }
+      let previousNode: IXmlElement; // needs a null check when accessed because of node index 0!
       for (let xmlNodeIndex: number = 0; xmlNodeIndex < xmlMeasureListArr.length; xmlNodeIndex++) {
         const xmlNode: IXmlElement = xmlMeasureListArr[xmlNodeIndex];
+        if (xmlNodeIndex > 0) {
+          previousNode = xmlMeasureListArr[xmlNodeIndex - 1];
+        }
         if (xmlNode.name === "print") {
           const newSystemAttr: IXmlAttribute = xmlNode.attribute("new-system");
           if (newSystemAttr?.value === "yes") {
@@ -438,7 +442,7 @@ export class InstrumentReader {
               throw new MusicSheetReadingException(errorMsg + this.instrument.Name);
             }
           }
-          this.addAbstractInstruction(xmlNode, octavePlusOne);
+          this.addAbstractInstruction(xmlNode, octavePlusOne, previousNode);
           if (currentFraction.Equals(new Fraction(0, 1)) &&
             this.isAttributesNodeAtBeginOfMeasure(this.xmlMeasureList[this.currentXmlMeasureIndex], xmlNode)) {
             this.saveAbstractInstructionList(this.instrument.Staves.length, true);
@@ -893,8 +897,16 @@ export class InstrumentReader {
           }
         }
 
-        const clefInstruction: ClefInstruction = new ClefInstruction(clefEnum, clefOctaveOffset, line);
-        this.abstractInstructions.push([staffNumber, clefInstruction]);
+        // TODO problem: in saveAbstractInstructionList, this is always saved in this.currentStaffEntry.
+        //   so when there's a <forward> or <backup> instruction in <attributes> (which is unfortunate encoding), this gets misplaced.
+        //   so for now we skip it.
+        const skipClefInstruction: boolean =
+          previousNode?.elements("forward").length > 0 ||
+          previousNode?.elements("backup").length > 0;
+        if (!skipClefInstruction) {
+          const clefInstruction: ClefInstruction = new ClefInstruction(clefEnum, clefOctaveOffset, line);
+          this.abstractInstructions.push([staffNumber, clefInstruction]);
+        }
       }
     }
     if (attrNode.element("key") !== undefined && this.instrument.MidiInstrumentId !== MidiInstrument.Percussion) {