Merge CL9619 to main (fix CommonTokenStream.seek)

[git-p4: depot-paths = "//depot/code/antlr4/main/": change = 9620]

runtime/Java/src/org/antlr/v4/runtime/BufferedTokenStream.java

@@ -105,7 +105,13 @@ public class BufferedTokenStream<T extends Token> implements TokenStream {
     }
 
     @Override
-    public void seek(int index) { p = index; }
+    public void seek(int index) {
+        if (p == -1) {
+            setup();
+        }
+
+        p = index;
+    }
 
     @Override
     public int size() { return tokens.size(); }

runtime/Java/src/org/antlr/v4/runtime/CommonTokenStream.java

@@ -73,6 +73,14 @@ public class CommonTokenStream extends BufferedTokenStream<CommonToken> {
         }
     }
 
+    @Override
+    public void seek(int index) {
+        super.seek(index);
+        while (p < index) {
+            consume();
+        }
+    }
+
     @Override
     protected CommonToken LB(int k) {
         if ( k==0 || (p-k)<0 ) return null;