wayland: Move buffer copy into mime_data_list_add()

It makes it clearer who owns the memory, and more reasonable to free it on
failure in the creating function.

(and, of course, pacifies static analysis.)

src/video/wayland/SDL_waylanddatamanager.c

@@ -185,8 +185,16 @@ mime_data_list_add(struct wl_list* list,
 {
     int status = 0;
     size_t mime_type_length = 0;
-
     SDL_MimeDataList *mime_data = NULL;
+    void *internal_buffer = NULL;
+
+    if (buffer != NULL) {
+        internal_buffer = SDL_malloc(length);
+        if (internal_buffer == NULL) {
+            return SDL_OutOfMemory();
+        }
+        SDL_memcpy(internal_buffer, buffer, length);
+    }
 
     mime_data = mime_data_list_find(list, mime_type);
 
@@ -211,8 +219,10 @@ mime_data_list_add(struct wl_list* list,
         if (mime_data->data != NULL) {
             SDL_free(mime_data->data);
         }
-        mime_data->data = buffer;
+        mime_data->data = internal_buffer;
         mime_data->length = length;
+    } else {
+        SDL_free(internal_buffer);
     }
 
     return status;
@@ -264,18 +274,7 @@ int Wayland_data_source_add_data(SDL_WaylandDataSource *source,
                                  const void *buffer,
                                  size_t length) 
 {
-    int status = 0;
-    if (length > 0) {
-        void *internal_buffer = SDL_malloc(length);
-        if (internal_buffer == NULL) {
-            status = SDL_OutOfMemory();
-        } else {
-            SDL_memcpy(internal_buffer, buffer, length);
-            status = mime_data_list_add(&source->mimes, mime_type, 
-                                        internal_buffer, length);
-        }
-    }
-    return status;
+    return mime_data_list_add(&source->mimes, mime_type, buffer, length);
 }
 
 SDL_bool