Fixes crash when a file is deleted then redownloaded

app/src/main/java/us/shandian/giga/io/StoredFileHelper.java

@@ -315,6 +315,7 @@ public class StoredFileHelper implements Serializable {
             return false;
 
         if (this.isInvalid() || storage.isInvalid()) {
+            if (this.srcName == null || storage.srcName == null || this.srcType == null || storage.srcType == null) return false;
             return this.srcName.equalsIgnoreCase(storage.srcName) && this.srcType.equalsIgnoreCase(storage.srcType);
         }