Spellchecker - avoid AIIOBE

plugins/spellchecker/src/com/intellij/spellchecker/compress/Alphabet.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright 2000-2012 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 package com.intellij.spellchecker.compress;
 
 import org.jetbrains.annotations.NotNull;
@@ -43,6 +58,7 @@ public final class Alphabet {
   }
 
   public int add(char c) {
+    if(lastIndexUsed>=letters.length-1) return -1;
     lastIndexUsed++;
     letters[lastIndexUsed] = c;
     return lastIndexUsed;