CanvasContext::draw: flushAndSubmit when not drawing

Bug: 195081399
Test: manual + dumpsys gfxinfo

CanvasContext::draw has some conditions under which it will not draw. We
still need to flushAndSubmit to free scratch memory if there were
texture uploads this frame.

Change-Id: I60d230cd36bed310a3155e4f1ca647c99c13c4cd