wallet: Reset BerkeleyDB handle after connection fails

According to the BerkeleyDB docs, the DbEnv handle may not be accessed
after close() has been called. This change ensures that we create a new
handle after close() is called. This avoids a segfault when the first
connection attempt fails and then a second connection attempt tries to
call open() on the already closed DbEnv handle.

src/wallet/db.cpp

@@ -169,6 +169,7 @@ bool BerkeleyEnvironment::Open(bool retry)
                          S_IRUSR | S_IWUSR);
     if (ret != 0) {
         dbenv->close(0);
+        Reset();
         LogPrintf("BerkeleyEnvironment::Open: Error %d opening database environment: %s\n", ret, DbEnv::strerror(ret));
         if (retry) {
             // try moving the database env out of the way