more robust: avoid sporadic crash of JEditBuffer.tokenMarker.getMainRuleSet().getModeName();

--- a/src/Tools/jEdit/src/jedit_bibtex.scala	Sun May 02 17:38:49 2021 +0200
+++ b/src/Tools/jEdit/src/jedit_bibtex.scala	Sun May 02 20:51:21 2021 +0200
@@ -20,7 +20,7 @@
 
 import org.gjt.sp.jedit.Buffer
 import org.gjt.sp.jedit.textarea.{JEditTextArea, TextArea}
-import org.gjt.sp.jedit.syntax.{Token => JEditToken, TokenMarker, TokenHandler, ParserRuleSet}
+import org.gjt.sp.jedit.syntax.{Token => JEditToken, TokenMarker, TokenHandler}
 
 import sidekick.{SideKickParser, SideKickParsedData}
 
@@ -82,10 +82,10 @@
 
   /* line context */
 
-  private val context_rules = new ParserRuleSet("bibtex", "MAIN")
+  private val mode_rule_set = Token_Markup.mode_rule_set("bibtex")
 
   private class Line_Context(val context: Option[Bibtex.Line_Context])
-    extends TokenMarker.LineContext(context_rules, null)
+    extends TokenMarker.LineContext(mode_rule_set, null)
   {
     override def hashCode: Int = context.hashCode
     override def equals(that: Any): Boolean =
@@ -100,6 +100,8 @@
 
   class Token_Marker extends TokenMarker
   {
+    addRuleSet(mode_rule_set)
+
     override def markTokens(context: TokenMarker.LineContext,
         handler: TokenHandler, raw_line: Segment): TokenMarker.LineContext =
     {

--- a/src/Tools/jEdit/src/token_markup.scala	Sun May 02 17:38:49 2021 +0200
+++ b/src/Tools/jEdit/src/token_markup.scala	Sun May 02 20:51:21 2021 +0200
@@ -22,6 +22,9 @@
 {
   /* line context */
 
+  def mode_rule_set(mode: String): ParserRuleSet =
+    new ParserRuleSet(mode, "MAIN")
+
   object Line_Context
   {
     def init(mode: String): Line_Context =
@@ -50,7 +53,7 @@
       val mode: String,
       val context: Option[Scan.Line_Context],
       val structure: Line_Structure)
-    extends TokenMarker.LineContext(new ParserRuleSet(mode, "MAIN"), null)
+    extends TokenMarker.LineContext(mode_rule_set(mode), null)
   {
     def get_context: Scan.Line_Context = context.getOrElse(Scan.Finished)
 
@@ -216,6 +219,8 @@
     protected val mode: String,
     protected val opt_buffer: Option[Buffer]) extends TokenMarker
   {
+    addRuleSet(mode_rule_set(mode))
+
     override def hashCode: Int = (mode, opt_buffer).hashCode
     override def equals(that: Any): Boolean =
       that match {