empty image window opens in several situations

[richlv]

last known tested version where the problem was not present : 7347
first known tested version where the problem is present : 7480

there are 3 scenarios that might or might not have the same cause :

(1)
open gpx
import image, correlate
open image window
delete both layers
open gpx
import image - notice how an empty image window opens together with the correlation dialog

(2)
open gpx
import image, correlate
open image window
close image window
delete image layer
notice how an empty image window opens

(3)
open gpx
import image, correlate
open image window
close image window
close josm
start josm
open gpx
import image - notice how an empty image window opens together with the correlation dialog

Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2014-10-21 19:23:06
Last Changed Author: Don-vip
Revision: 7643
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Relative URL: ^/trunk
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2014-10-21 21:19:16 +0200 (Tue, 21 Oct 2014)
Last Changed Rev: 7643

Identification: JOSM/1.5 (7643 en_GB) Linux openSUSE 13.1 (Bottle) (x86_64)
Memory Usage: 176 MB / 683 MB (30 MB allocated, but free)
Java version: 1.7.0_51, Oracle Corporation, OpenJDK 64-Bit Server VM
Java package: java-1_7_0-openjdk:x86_64-1.7.0.6
VM arguments: [-Djava.net.useSystemProxies=true]
Dataset consistency test: No problems found

Plugins:
- InfoMode (30737)
- PicLayer (30762)
- imagery_offset_db (30762)
- measurement (30737)
- notes (v0.9.4)
- pbf (30762)
- reverter (30737)
- terracer (30737)

[Don-vip]

In 7660/josm:

fix #10672 - empty image window opens in several situations (regression from r7444)