Don't check for null references.

The address of a reference will never be null in well formed C++ code.
The function returning the value being checked simply returns a
dereferenced pointer (which is just going to segfault if it is null!).

Change-Id: I3a4eb6adfc003c63ebf21b81d46088d52154d99d
[HWUI]: Bind wrong VBO when drawing text

Symptom:
We should not set mDrawn to true if we have no GL draw call.

Root Cause:
In some case, issueDrawCommand may executed without GL draw call.
It may miss the unbindMeshBuffer in the next issueDrawCommand and the status of VBO of FontRenderer will incorrect.

Solution:
Add condition to check if have draw call.

Change-Id: I9e96cd0334c515172b0ed6c25b101c81cf6d2e6f