Add fallback case to layers_extensions.cpp

Bug: http://b/79940628

Test: cts-tradefed run commandAndExit cts -m CtsGpuToolsHostTestCases

Change-Id: I5b15e9dbf4bc9887901f584741980c1eca3252a7
Merged-In: I9f4ffb6b3afa8c4b8048e1d579c1befbb6565e19
1 file changed