Fixed: Improper tie resolution

This commit fixes a problem where ties would not be encoded correctly. It was fixed by adding an extra parameter to the tie resolution dictionary to further differentiate ties on different staves.

It also uses the concatenation operator instead of the addition operator. *facepalm*.

src/ExportGenerators.mss

@@ -964,7 +964,7 @@ function GenerateNote (nobj) {
 
     // construct an index that will be used to open a tie, or check if a tie is open.
     // this may be modified below if the tie extends to the next bar
-    tie_idx = parent_bar.BarNumber + '-' + nobj.ParentNoteRest.VoiceNumber + '-' + pnum;
+    tie_idx = parent_bar.BarNumber & '-' & staff & '-' & nobj.ParentNoteRest.VoiceNumber & '-' & pnum;
 
     if (tie_resolver.PropertyExists(tie_idx) and tie_resolver[tie_idx] != null)
     {
@@ -982,7 +982,7 @@ function GenerateNote (nobj) {
         assume that it stretches to this bar. Look backwards to see if this is the case
         and set it as the end of the tie.
     */
-    prev_tie_idx = (parent_bar.BarNumber - 1) + '-' + nobj.ParentNoteRest.VoiceNumber + '-' + pnum;
+    prev_tie_idx = (parent_bar.BarNumber - 1) & '-' & staff & '-' & nobj.ParentNoteRest.VoiceNumber & '-' & pnum;
 
     if (tie_resolver.PropertyExists(prev_tie_idx) and tie_resolver[prev_tie_idx] != null)
     {
@@ -1006,7 +1006,7 @@ function GenerateNote (nobj) {
         // bar by one so that we can pick up on it later...
         if (tie_dur >= parent_bar.Length)
         {
-            tie_idx = (parent_bar.BarNumber + 1) + '-' + nobj.ParentNoteRest.VoiceNumber + '-' + pnum;
+            tie_idx = (parent_bar.BarNumber + 1) & '-' & staff & '-' & nobj.ParentNoteRest.VoiceNumber & '-' & pnum;
         }
 
         tie_resolver[tie_idx] = tie._id;