improve wall filter

src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlLexer.java

@@ -357,6 +357,10 @@ public class MySqlLexer extends Lexer {
             }
 
             for (;;) {
+                if (ch == EOI) {
+                    this.token = Token.ERROR;
+                    return;
+                }
                 if (ch == '*' && charAt(pos + 1) == '/') {
                     bufPos += 2;
                     scanChar();

src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java

@@ -189,7 +189,8 @@ public class MySqlStatementParser extends SQLStatementParser {
     }
 
     public SQLSelectStatement parseSelect() {
-        return new SQLSelectStatement(new MySqlSelectParser(this.exprParser).select());
+        MySqlSelectParser selectParser = new MySqlSelectParser(this.exprParser);
+        return new SQLSelectStatement(selectParser.select());
     }
 
     public SQLUpdateStatement parseUpdateStatement() {