This was detected while running the tests with the -Wconditional-uninitialized flag./autogen.sh CC=clang CFLAGS="-Wconditional-uninitialized" ./configure make check
The resulting warning is a false positive, but setting the value to -1
ensures that the CHECK below will fail if recid is never written to.
This is a backport of secp256k1#889
It should allow us to finally land D9110