wayland: Fix primary selection handling when the protocol isn't supported

The primary selection protocol is optional, so the function pointers to the internal Wayland functions should only be set if the protocol is supported. This allows graceful fall-back to the generic SDL implementation in other cases.

Fixes the clipboard tests under Weston.

src/video/wayland/SDL_waylandclipboard.c

@@ -107,7 +107,7 @@ int Wayland_SetPrimarySelectionText(SDL_VideoDevice *_this, const char *text)
 {
     SDL_VideoData *video_data = _this->driverdata;
     SDL_WaylandPrimarySelectionDevice *primary_selection_device = NULL;
-    int status = 0;
+    int status = -1;
 
     if (video_data->input != NULL && video_data->input->primary_selection_device != NULL) {
         primary_selection_device = video_data->input->primary_selection_device;

src/video/wayland/SDL_waylandvideo.c

@@ -230,9 +230,6 @@ static SDL_VideoDevice *Wayland_CreateDevice(void)
     device->SetClipboardData = Wayland_SetClipboardData;
     device->GetClipboardData = Wayland_GetClipboardData;
     device->HasClipboardData = Wayland_HasClipboardData;
-    device->SetPrimarySelectionText = Wayland_SetPrimarySelectionText;
-    device->GetPrimarySelectionText = Wayland_GetPrimarySelectionText;
-    device->HasPrimarySelectionText = Wayland_HasPrimarySelectionText;
     device->StartTextInput = Wayland_StartTextInput;
     device->StopTextInput = Wayland_StopTextInput;
     device->SetTextInputRect = Wayland_SetTextInputRect;
@@ -912,6 +909,12 @@ int Wayland_VideoInit(SDL_VideoDevice *_this)
 
     Wayland_InitKeyboard(_this);
 
+    if (data->primary_selection_device_manager) {
+        _this->SetPrimarySelectionText = Wayland_SetPrimarySelectionText;
+        _this->GetPrimarySelectionText = Wayland_GetPrimarySelectionText;
+        _this->HasPrimarySelectionText = Wayland_HasPrimarySelectionText;
+    }
+
     data->initializing = SDL_FALSE;
 
     return 0;