Fixes build warning introduced by #10155
In file included from ./wallet/db.h:9:0,
from ./wallet/walletdb.h:11,
from wallet/wallet.h:18,
from init.cpp:44:
./clientversion.h:14:48: warning: missing terminating ' character
#error Client version information missing: wasn't defined by bitcoin-config.h nor defined any other way
^
repeated many times in the build. @laanwj