Added cacheHandler checking (#253)

+ Added check in CdnManager.java
+ Added check in AudioFileStreaming.java

Author: jordi735

lib/src/main/java/xyz/gianlu/librespot/audio/cdn/CdnManager.java

@@ -345,9 +345,11 @@ public void close() {
                 super.close();
                 executorService.shutdown();
 
-                try {
-                    cacheHandler.close();
-                } catch (IOException ignored) {
+                if (cacheHandler != null) {
+                    try {
+                        cacheHandler.close();
+                    } catch (IOException ignored) {
+                    }
                 }
             }
 

lib/src/main/java/xyz/gianlu/librespot/audio/storage/AudioFileStreaming.java

@@ -157,9 +157,11 @@ public void close() {
         if (chunksBuffer != null)
             chunksBuffer.close();
 
-        try {
-            cacheHandler.close();
-        } catch (IOException ignored) {
+        if (cacheHandler != null) {
+            try {
+                cacheHandler.close();
+            } catch (IOException ignored) {
+            }
         }
     }