- fixes possible problem while saving screenshots

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Bug fixes for:
* Interface:
* Excessive delay occurred when typing into labels in long projects.
* Last digit of TimeText controls could not be manipulated in some formats.
* (Windows, OS X) Play and Record shortcuts did not work after clicking in Device Toolbar.
* (OS X, Linux) Crash occurred if Toolbars were reset during playback or recording.
* Imports and Exports:
* MP2 files were not importable without FFmpeg library or an import rule.
* Files that could only be imported using FFmpeg imported as noise with no error message if FFmpeg was not available.
* Files containing PCM audio but an incorrect extension (such as MP3) caused a freeze.
* Effects and Analysis:
* An empty command could be added to a Chain which then displayed a Nyquist error message when run.
* Plot Spectrum didn’t preserve signal level if multiple tracks were analyzed.
* Other bug fixes:
* Audacity has been provisionally fixed so that it can no longer create block files longer than the sample format or project format allows, and can no longer delete these, which led to data loss. Any overlong blocks found are preserved but “orphaned”, so will appear as silence.
* Orphan block files were wrongly reported if cutting or copying to the clipboard then reopening the project in the same session.
* Fixed some crashes and incorrect movement of audio when dragging tracks.
* (Windows) Data loss is now prevented when encountering a corrupted .aup file created in ANSI builds.
* (Linux) Restore building if USE_PORTMIXER is not defined.
Changes and Improvements:
* Normalize: Faster processing and improved interface. Left-right balance in unsplit stereo tracks is now preserved by default, with a checkbox option provided to process stereo channels independently.
* Spectrograms now allow window sizes up to 32768 and frequencies up to half the sample rate (the maximum possible).
* Mix and Render now preserves clip length by not rendering white space between time zero and first audio, and preserves audio before time zero. To retain silence before the audio starts, generate silence after render.
* Grouped some Edit Menu items into “Remove Audio” and “Clip Boundaries”.
* CleanSpeech Mode removed from Interface Preferences (it still runs if it was enabled in a previous Audacity but can only be turned off there).
* (OS X) Added support for AudioUnit MusicEffects (but no MIDI support).
* (Linux) Set the per-user files directory per the program name set in configure.

GUI Improved: save the heights of task list pane and Torrent History pane separately

GUI Improved: keep the tasks which occur downloading error together when sort task list by state

GUI Improved: add confirm dialog when restore the display of hidden torrents in Peer Share list

GUI Bugfix: Auto-Shutdown at specified time does not work

GUI Bugfix: open URL using system default browser instead of IE

GUI Bugfix: torrent file icon should not use the program icon

GUI Bugfix: when adding new Torrent, all files will be downloaded instead of only selected

GUI Bugfix: task position in the task list should not be changed when press Home/End

GUI Bugfix: the setting of View - Task list - Show filter does not work when program starts

Core Bugfix: handle torrent file not using UTF-8 encoding