Infinite loop in download window on OutOfMemory

[Zverikk]

When OOM happens and user presses download button, a message appears concerning the OOM error. And again, and again. Seems like there's one for every tile downloaded from OSM. There is no chance to click through all these dialogs, close download window and save changes made.

User should have a chance to save his work even when there is an error.

[Zverikk]

part of console:

Autosave failed:
java.lang.OutOfMemoryError: Java heap space
java.lang.OutOfMemoryError: Java heap space
Exception occurred during event dispatching:
Exception occurred during event dispatching:
java.lang.OutOfMemoryError: Java heap space
Exception occurred during event dispatching:Exception occurred during event disp
atching:
Exception occurred during event dispatching:
Exception occurred during event dispatching:
Exception occurred during event dispatching:
java.lang.OutOfMemoryError: Java heap space
Exception occurred during event dispatching:
java.lang.OutOfMemoryError: Java heap space
Exception occurred during event dispatching:
java.lang.OutOfMemoryError: Java heap space
Exception occurred during event dispatching:
java.lang.OutOfMemoryError: Java heap space
Autosave failed:
java.lang.OutOfMemoryError: Java heap space

(later) on the next run, JOSM found 4 autosaves. Thank you for that feature. You should probably notify user somehow that there are autosaves, so he/she does not panic :)