Fix NPE in FileMergeCacheManager
Found this NPE while looking at test failures
```
java.lang.NullPointerException
at com.facebook.presto.cache.filemerge.FileMergeCacheManager.getCacheScopeSizeInBytes(FileMergeCacheManager.java:222)
at com.facebook.presto.cache.filemerge.FileMergeCacheManager.lambda$null$3(FileMergeCacheManager.java:158)
```
@@ -219,6 +219,9 @@ public class FileMergeCacheManager
long bytes = 0;
for (Path path : paths) {
CacheRange cacheRange = persistedRanges.get(path);
+ if (cacheRange == null) {
+ continue;
+ }
Lock readLock = cacheRange.getLock().readLock();
readLock.lock();
try {
