Delete multichunk from cache if decryption failed. Related to #59

syncany-lib/src/main/java/org/syncany/operations/Downloader.java

@@ -91,7 +91,7 @@ public void downloadAndDecryptMultiChunks(Set<MultiChunkId> unknownMultiChunkIds
 					logger.log(Level.FINE, "    -> FAILED: Decryption/extraction of multichunk failed, deleting " + multiChunkId + " ...");
 					localDecryptedMultiChunkFile.delete();
 
-					throw new IOException("Multichunk decryption/extraction failed. The multichunk might have been tampered with!", e);
+					throw new IOException("Decryption/extraction of multichunk " + multiChunkId + " failed. The multichunk might have been tampered with!", e);
 				}
 				finally {
 					logger.log(Level.FINE, "  + Locally deleting multichunk " + multiChunkId + " ...");