[cogl-texture] Fix the count for the number of enabled arrays
[cogl-texture] Fix the count for the number of enabled arrays

The quad drawing code keeps track of the number of texture units that
have the tex coord array enabled so that in the next call it can
disabled any that are no longer enabled. However it was using 'i+1' as
the count but 'i' is already set to 'n_layers' from the previous for
loop.

Therefore it was disabling an extra texture unit. This doesn't
normally matter but it was causing GLES 2 to pointlessly realize an
extra unit.

Distrotech/cogl,Distrotech/cogl,spatulasnout/cogl,djdeath/cogl-android,Distrotech/cogl,gcampax/cogl,djdeath/cogl,djdeath/cogl,Distrotech/cogl,gcampax/cogl,djdeath/cogl-android,djdeath/cogl,collects/cogl,gcampax/cogl,djdeath/cogl-android,collects/cogl,spatulasnout/cogl,gcampax/cogl