Fix incorrect this.channel access

nextTokenOnChannel was accessing the field `this.channel` instead of the
parameter `channel`. The buffered token stream class doesn't have a field
named `channel`, so this exhausted the token buffer instead.

The bug had not been caught because it is only called from `CommonTokenStream`
with parameter `this.channel`.

Signed-off-by: Phlosioneer <mattmdrr2@gmail.com>

runtime/JavaScript/src/antlr4/BufferedTokenStream.js

@@ -253,7 +253,7 @@ export default class BufferedTokenStream extends TokenStream {
 			return -1;
 		}
 		let token = this.tokens[i];
-		while (token.channel !== this.channel) {
+		while (token.channel !== channel) {
 			if (token.type === Token.EOF) {
 				return -1;
 			}