Fix RDP connect crash on Windows: initialize FreeRDP signal handling

Every reference FreeRDP client (X11, Windows, macOS, SDL, Wayland, Android)
calls freerdp_handle_signals() once at startup before connecting. OrbitHub
never did. On Windows this is the only place that initializes a global
CRITICAL_SECTION used internally by freerdp_add_signal_cleanup_handler(),
which freerdp_connect() calls automatically. Skipping it leaves that lock
zero-initialized -- invalid on Windows, but silently tolerated on POSIX,
which is why this never surfaced in Linux testing. The result was a crash
(access violation inside EnterCriticalSection) on every RDP connect attempt
on Windows. Call it once, guarded, before the first connection.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/rdp_session_backend.cpp

@@ -7,6 +7,7 @@
 
 #include <cmath>
 #include <cstring>
+#include <mutex>
 #include <new>
 #include <utility>
 
@@ -31,12 +32,32 @@
 #include <freerdp/locale/keyboard.h>
 #include <freerdp/scancode.h>
 #include <freerdp/settings.h>
+#include <freerdp/utils/signal.h>
 #include <winpr/crt.h>
 #include <winpr/synch.h>
 #include <winpr/user.h>
 #endif
 
 namespace {
+
+#ifdef ORBITHUB_HAS_FREERDP
+// Every reference FreeRDP client (X11, Windows, macOS, SDL, Wayland,
+// Android) calls this once at startup before connecting. On Windows it's
+// the only place that initializes a global CRITICAL_SECTION used by
+// freerdp_add_signal_cleanup_handler(); skipping it leaves that lock
+// zero-initialized (invalid on Windows, tolerated on POSIX), so the first
+// freerdp_connect() crashes with a null-pointer dereference inside
+// EnterCriticalSection. Guarded so it only ever runs once.
+void ensureFreeRdpSignalHandlersInitialized()
+{
+    static std::once_flag onceFlag;
+    std::call_once(onceFlag, []() {
+        const int rc = freerdp_handle_signals();
+        Q_UNUSED(rc);
+    });
+}
+#endif
+
 constexpr int kDefaultDesktopWidth = 1280;
 constexpr int kDefaultDesktopHeight = 720;
 constexpr int kMinDesktopWidth = 640;
@@ -1472,6 +1493,8 @@ void RdpSessionBackend::workerMain()
     m_workerRunning.store(false);
     return;
 #else
+    ensureFreeRdpSignalHandlersInitialized();
+
     freerdp* instance = freerdp_new();
     if (instance == nullptr) {
         emitConnectionFailureAsync(QStringLiteral("Failed to initialize FreeRDP runtime."),