deleting mapillary layer during download blocks interface

[richlv]

download an area with a larger number of mapillary sequences.
add mapillary imagery layer and quickly, while it is still downloading, delete this layer.
interface is completely blocked and josm is unusable. even though the mapillary layer disappears a bit later, interface is still unusable.

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2017-11-12 02:32:10 +0100 (Sun, 12 Nov 2017)
Build-Date:2017-11-12 02:38:47
Revision:13115
Relative:URL: ^/trunk

Identification: JOSM/1.5 (13115 en) Linux openSUSE Leap 42.1 (x86_64)
Memory Usage: 312 MB / 683 MB (96 MB allocated, but free)
Java version: 1.8.0_121-b13, Oracle Corporation, OpenJDK 64-Bit Server VM
Screen: :0.0 1440x900
Maximum Screen Size: 1440x900
Java package: java-1_8_0-openjdk:x86_64-1.8.0.121
VM arguments: [-Djava.net.useSystemProxies=true]

Plugins:
+ ColumbusCSV (33577)
+ InfoMode (33722)
+ Mapillary (v1.5.8)
+ PicLayer (33385)
+ apache-commons (33668)
+ apache-http (32699)
+ graphview (33004)
+ imagery_offset_db (33774)
+ jna (32699)
+ log4j (32699)
+ measurement (33760)
+ pbf (33568)
+ photo_geotagging (33494)
+ photoadjust (33746)
+ reverter (33572)

Map paint styles:
- https://josm.openstreetmap.de/josmfile?page=Styles/Lane_and_Road_Attributes&zip=1

Last errors/warnings:
- W: No configuration settings found.  Using hardcoded default values for all pools.

[Don-vip]

Closed as duplicate of #17864.