Remove error from startup_regtest when loading wallet

startup_regtest now checks if wallet directory exists before creating
the default wallet, then it will check if wallet is loaded before
attempting to load it. This prevents unnecessary errors during the
execution of this bash script.

[ Squashed fixup: `regtest: restore double quotes on PATH_TO_BITCOIN` -- RR ]

contrib/startup_regtest.sh

@@ -142,18 +142,25 @@ start_ln() {
 	# Wait for it to start.
 	while ! bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest ping 2> /tmp/null; do echo "awaiting bitcoind..." && sleep 1; done
 
-	# Kick it out of initialblockdownload if necessary
-	if bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest getblockchaininfo | grep -q 'initialblockdownload.*true'; then
-		# Modern bitcoind needs createwallet
+	# Check if default wallet exists
+	if ! bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest listwalletdir | jq -r '.wallets[] | .name' | grep -wqe 'default' ; then
+		# wallet dir does not exist, create one
 		echo "Making \"default\" bitcoind wallet."
 		bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest createwallet default >/dev/null 2>&1
-		# But it might already exist, load it
-	        bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest loadwallet default
+	fi
+
+	# Check if default wallet is loaded
+	if ! bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest listwallets | jq -r '.[]' | grep -wqe 'default' ; then
+		echo "Loading \"default\" bitcoind wallet."
+		bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest loadwallet default >/dev/null 2>&1
+	fi
+
+	# Kick it out of initialblockdownload if necessary
+	if bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest getblockchaininfo | grep -q 'initialblockdownload.*true'; then
 		bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest generatetoaddress 1 "$(bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest getnewaddress)" > /dev/null
-	else
-		bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest loadwallet default
 	fi
-	alias bt-cli='bitcoin-cli -datadir=$PATH_TO_BITCOIN -regtest'
+
+	alias bt-cli='bitcoin-cli -datadir="$PATH_TO_BITCOIN" -regtest'
 
 	if [ -z "$1" ]; then
 		nodes=2