COMP: QuadrilateralCell Out-of-bounds-write.

From Coverity Scan:

  CID 1081058 (#2-1 of 4): Out-of-bounds write (OVERRUN)
  CID 1081058 (#3 of 4): Out-of-bounds write (OVERRUN)
  CID 1081058 (#4 of 4): Out-of-bounds write (OVERRUN)
  6. overrun-local: Overrunning array of 2 4-byte elements at element index 2
     (byte offset 8) by dereferencing pointer "x + j".

Change-Id: Ic3669d48624559509f594dc7f82f4caa2cd1b601
Merge topic 'coverity_quad'

7858bb8 COMP: QuadrilateralCell Out-of-bounds-write.