bugfix: make LoadWallet assigns status always

Although loadwallet() in rpcwallet.cpp assumes LoadWallet() always
assign some value to the 'status', but LoadWallet() does not do so
in some situation.

This fixes above and prevends loadwallet() returns ambiguous error code.

src/wallet/db.h

@@ -212,6 +212,7 @@ enum class DatabaseStatus {
     FAILED_ALREADY_EXISTS,
     FAILED_NOT_FOUND,
     FAILED_CREATE,
+    FAILED_LOAD,
     FAILED_VERIFY,
     FAILED_ENCRYPT,
 };