Add fallback case to layers_extensions.cpp

Bug: http://b/79940628

Test: cts-tradefed run commandAndExit cts -m CtsGpuToolsHostTestCases

Change-Id: If1485e3f845b781464eca9c6d2a6453baf61a4f5
Merged-In: I2881ff08cce5c129fd4b261814462d71d2c29a89
4 files changed