Make SVDFile.from_builtin() handle missing or bad svd zip.
Make SVDFile.from_builtin() handle missing or bad svd zip.

- A warning will be printed instead of letting pyocd die.

mbedmicro/pyOCD,flit/pyOCD,mesheven/pyOCD,pyocd/pyOCD,pyocd/pyOCD,mbedmicro/pyOCD,mesheven/pyOCD,mesheven/pyOCD,mbedmicro/pyOCD,flit/pyOCD