Check if the cache is already empty before trying to evict more span

This case may happen if the max span size is more than the max size the
evictor is configured.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=169101093

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/LeastRecentlyUsedCacheEvictor.java

@@ -74,7 +74,7 @@ public final class LeastRecentlyUsedCacheEvictor implements CacheEvictor, Compar
   }
 
   private void evictCache(Cache cache, long requiredSpace) {
-    while (currentSize + requiredSpace > maxBytes) {
+    while (currentSize + requiredSpace > maxBytes && !leastRecentlyUsed.isEmpty()) {
       try {
         cache.removeSpan(leastRecentlyUsed.first());
       } catch (CacheException e) {

library/core/src/test/java/com/google/android/exoplayer2/upstream/cache/LeastRecentlyUsedCacheEvictorTest.java

+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * 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.google.android.exoplayer2.upstream.cache;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mockito;
+import org.mockito.MockitoAnnotations;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+/**
+ * Unit tests for {@link LeastRecentlyUsedCacheEvictor}.
+ */
+@RunWith(RobolectricTestRunner.class)
+@Config(sdk = Config.TARGET_SDK, manifest = Config.NONE)
+public class LeastRecentlyUsedCacheEvictorTest {
+
+  @Before
+  public void setUp() throws Exception {
+    MockitoAnnotations.initMocks(this);
+  }
+
+  @Test
+  public void testContentBiggerThanMaxSizeDoesNotThrowException() throws Exception {
+    int maxBytes = 100;
+    LeastRecentlyUsedCacheEvictor evictor = new LeastRecentlyUsedCacheEvictor(maxBytes);
+    evictor.onCacheInitialized();
+    evictor.onStartFile(Mockito.mock(Cache.class), "key", 0, maxBytes + 1);
+  }
+
+}