fix thumbnailExists false for encrypted

iOSClient/Utility/CCUtility.m

@@ -986,7 +986,7 @@
         
         // thumbnailExists
             
-        if([ext isEqualToString:@"JPG"] || [ext isEqualToString:@"PNG"] || [ext isEqualToString:@"JPEG"] || [ext isEqualToString:@"GIF"] || [ext isEqualToString:@"BMP"] || [ext isEqualToString:@"MP3"]  || [ext isEqualToString:@"MOV"]  || [ext isEqualToString:@"MP4"]  || [ext isEqualToString:@"M4V"] || [ext isEqualToString:@"3GP"])
+        if (([ext isEqualToString:@"JPG"] || [ext isEqualToString:@"PNG"] || [ext isEqualToString:@"JPEG"] || [ext isEqualToString:@"GIF"] || [ext isEqualToString:@"BMP"] || [ext isEqualToString:@"MP3"]  || [ext isEqualToString:@"MOV"]  || [ext isEqualToString:@"MP4"]  || [ext isEqualToString:@"M4V"] || [ext isEqualToString:@"3GP"]) && metadata.encrypted == NO)
             metadata.thumbnailExists = YES;
         else
             metadata.thumbnailExists = NO;