fix(renderer): Gracefully handle null image textures (#9600) 7dd9f91b4a

Core problem: The android runtime updates out-of-band assets on the main
thread, while rendering and texture updates happen on the worker thread.
This led to a race condition where the RenderImage could still have a
pending texture update while drawing a frame, meaning its current
texture was null.

Short term fix: Just don't draw RiveRenderImages if their texture is
null.

NOTE: This doesn't fix the general race condition where data is
simultaneously being read and written by different threads, but as long
as we cross our fingers and hope that pointer writes are atomic (an
assumption that must also be true for other types of OOB assets being
written), the null check will help us limp by until we rearchitect the
threading model, which is now a very high priority item.

Author: csmartdalton

.rive_head

@@ -1 +1 @@
-3df92e66a45589d9114de55ecbfea494a068198f
+7dd9f91b4a52ae24f6c606ad62dcc4a46dbec32d