fix(Dolphin): guard netplay includes against missing SFML dependency

NetPlayClient.h requires SFML/Network/Packet.hpp. When the dolphin-ios
submodule is present but SFML headers are not in the search path the build
fails. Add __has_include(<SFML/Network/Packet.hpp>) to the guard so the
C++ netplay implementation is only compiled when all dependencies exist.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: JoeMatt

Cores/Dolphin/PVDolphinCore/Core/PVDolphinCore+Netplay.mm

@@ -30,7 +30,7 @@
 // NetPlay headers depending on the Dolphin revision.
 // ---------------------------------------------------------------------------
 
-#if __has_include("Core/NetPlayClient.h")
+#if __has_include("Core/NetPlayClient.h") && __has_include(<SFML/Network/Packet.hpp>)
     #define HAVE_DOLPHIN_NETPLAY 1
     #include "Core/NetPlayClient.h"
     #include "Core/NetPlayServer.h"