Gallery2: Fix Gallery2 ANR when run monkey

When we create ExportDialog View,a null pointer
is used to reset mOriginalBounds which cause
this bug happened.

Add a condition when judge conditon is  null,then
not to reset mOriginalBounds to avoid this bug.

CRs-fixed: 647207

Change-Id: If91434c3ca15a287600097b7a5ec8c5aa7d7d6e2