[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