Don't call moveParagraph() with null |VisiblePositon|

Don't call moveParagraph() with null |VisiblePositon|

This patch changes |IndentOutdentCommand::outdentParagraph()| not to call
|CompositeEditCommand::movePargrap()| with null |VisiblePositon|.

This situation can be happened in attached test case, where
|visibleStartOfParagraph| and |visibleEndOfPargraph| are second TABLE element.
Both |startOfParagraph()| and |endOfParagraph()| return null |VisiblePositon|
for them.

BUG=379058
TEST=editing/execCommand/outdent-collapse-table-crash-2.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175258

[yosin_UTC9, 2014-06-02 00:49:03]

Could you review this patch?
Thanks in advance.

Note: Compilation failures of mac_blink_rel, blink_android_compile_{dbg,rel}
aren't related to this patch.

[Yuta Kitamura, 2014-06-02 06:22:21]

lgtm

[yosin_UTC9, 2014-06-02 06:49:55]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2014-06-02 06:50:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/yosin@chromium.org/305143002/20001

[commit-bot: I haz the power, 2014-06-02 08:51:10]

Change committed as 175258