Fix #121108: Improved Poll Function for IMAGE_OT_clipboard_paste

Ensure that the current area is an Image Editor before allowing
clipboard paste, since that will fail.

Pull Request: https://projects.blender.org/blender/blender/pulls/121142

source/blender/editors/space_image/image_ops.cc

@@ -3009,6 +3009,12 @@ static int image_clipboard_paste_exec(bContext *C, wmOperator *op)
 
 static bool image_clipboard_paste_poll(bContext *C)
 {
+  SpaceImage *sima = CTX_wm_space_image(C);
+  if (!sima) {
+    CTX_wm_operator_poll_msg_set(C, "Image Editor not found");
+    return false;
+  }
+
   if (!WM_clipboard_image_available()) {
     CTX_wm_operator_poll_msg_set(C, "No compatible images are on the clipboard");
     return false;