surfaceflinger: fix captureScreen for landscape LCM

Make DisplayRenderArea::getSourceCrop return the display scissor
when the source crop is empty.  Force the source crop to be empty in
captureScreen.  This makes sure the install orientation is applied
on the source crop once, not twice.

Bug: 113041375
Test: force primaryDisplayOrientation, rotate screen, and switch
      apps
Change-Id: I15006f867ff2d4a92ebccb1334ce59ab32abe69a
Merged-In: I15006f867ff2d4a92ebccb1334ce59ab32abe69a