fix: handle invalid rpcbind port earlier

Previously, when an invalid port was specified
in `-rpcbind`, the `SplitHostPort()` return value
in `HTTPBindAddresses()` was ignored and attempt
would be made to bind to the default rpcbind port
(with the host/port treated as a host).

This rearranges port checking code in
`AppInitMain()` to handle the invalid
port before reaching `HTTPBindAddresses()`.

Also adjusts associated functional tests.

src/init.cpp

@@ -1279,6 +1279,9 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     RegisterZMQRPCCommands(tableRPC);
 #endif
 
+    // Check port numbers
+    if (!CheckHostPortOptions(args)) return false;
+
     /* Start the RPC server already.  It will be started in "warmup" mode
      * and not really process calls already (but it will signify connections
      * that the server is there and will be ready later).  Warmup mode will
@@ -1369,9 +1372,6 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         validation_signals.RegisterValidationInterface(fee_estimator);
     }
 
-    // Check port numbers
-    if (!CheckHostPortOptions(args)) return false;
-
     for (const std::string& socket_addr : args.GetArgs("-bind")) {
         std::string host_out;
         uint16_t port_out{0};