[WK2] Fix for crash issue while destroying ImageBuffer

[WK2] Fix for crash issue while destroying ImageBuffer

[Title] Fix for crash issue while destroying ImageBuffer
[issue#] Web-2975
[Problem] crash while go back to previous page
[Cause] While destroying ImageBuffer we just calling cairo_surface_destroy, but we not calling
cairo_surface_flush. Since cairo_surface_flush is getting called some times after destroying cairo_surface by cairo internally which leads to crash.
[Solution] calling cairo_surface_flush before destroying cairo_surface_destroy.
[Developer] shanmuga.m

Change-Id: I59932e2c2547e902a388165f5d8bf6b2763aead4