Tweak var table sort order

Still primarily ascending numeric order, but now we use the symbol
type as the secondary sort instead of the label.

Also, fix References crash on first line of empty var table.

SourceGen/LineListGen.cs

@@ -1345,9 +1345,12 @@ namespace SourceGen {
             }
             int tableIndex = line.SubLineIndex;
             if (lvt.ClearPrevious) {
-                if (--tableIndex < 0) {
+                tableIndex--;
-                    return null;
+            }
-                }
+            if (tableIndex < 0 || tableIndex >= lvt.Count) {
+                // Will be -1 on first line when ClearPrevious was set.  Will be zero on
+                // first line of empty table.
+                return null;
             }
 
             return lvt[tableIndex];

SourceGen/LocalVariableTable.cs

@@ -112,15 +112,22 @@ namespace SourceGen {
 
         private void SortIfNeeded() {
             if (mNeedSort) {
-                // Currently sorting primarily by value, secondarily by label.  This ordering
+                // Currently sorting primarily by value, secondarily by symbol type.  This
-                // determines how it appears in the code list.  If we want to make it
+                // ordering determines how it appears in the code list.  If we want to make it
                 // configurable we just need to replace the sort function.
                 mVarByValue.Sort((a, b) => {
+                    // Numeric ascending.
                     int diff = a.Value - b.Value;
                     if (diff != 0) {
                         return diff;
                     }
-                    return a.Label.CompareTo(b.Label);
+                    // DP addr first, StackRel const second
+                    if (a.SymbolType == Symbol.Type.ExternalAddr) {
+                        return -1;
+                    } else {
+                        return 1;
+                    }
+                    //return a.Label.CompareTo(b.Label);
                 });
                 mNeedSort = false;
             }