Fix #108746: Defaults / Save startup file don't save the window size.

Hopefully now the behavior is fully consistent with before the refactor,
current implemented one by this commit:

- When loading factory settings file on startup, go full-screen.
- In all other startup cases, use size as stored in the startup .blend
  file.

Regression from ebb5643e59 and 32bbfbb06e.

source/blender/blenloader/BLO_readfile.h

@@ -76,7 +76,10 @@ typedef struct BlendFileReadWMSetupData {
   /** The existing WM when filereading process is started. */
   struct wmWindowManager *old_wm;
 
+  /** The startup file is being read. */
   bool is_read_homefile;
+  /** The factory startup file is being read. */
+  bool is_factory_startup;
 } BlendFileReadWMSetupData;
 
 struct BlendFileReadParams {

source/blender/windowmanager/intern/wm_files.cc

@@ -190,6 +190,8 @@ static BlendFileReadWMSetupData *wm_file_read_setup_wm_init(bContext *C,
   wmWindowManager *wm = static_cast<wmWindowManager *>(bmain->wm.first);
   BlendFileReadWMSetupData *wm_setup_data = MEM_cnew<BlendFileReadWMSetupData>(__func__);
   wm_setup_data->is_read_homefile = is_read_homefile;
+  /* This info is not always known yet when this function is called. */
+  wm_setup_data->is_factory_startup = false;
 
   if (wm == nullptr) {
     return wm_setup_data;
@@ -404,10 +406,13 @@ static void wm_file_read_setup_wm_finalize(bContext *C,
   BLI_assert(wm_setup_data != nullptr);
   wmWindowManager *wm = static_cast<wmWindowManager *>(bmain->wm.first);
 
-  /* If reading home (startup) file, and there was no previous WM, clear the size of the windows in
+  /* If reading factory startup file, and there was no previous WM, clear the size of the windows
-   * newly read WM so that they get resized to occupy the whole available space on current monitor.
+   * in newly read WM so that they get resized to occupy the whole available space on current
+   * monitor.
    */
-  if (wm_setup_data->is_read_homefile && wm_setup_data->old_wm == nullptr) {
+  if (wm_setup_data->is_read_homefile && wm_setup_data->is_factory_startup &&
+      wm_setup_data->old_wm == nullptr)
+  {
     wm_clear_default_size(C);
   }
 
@@ -1352,6 +1357,7 @@ void wm_homefile_read_ex(bContext *C,
     BKE_reportf(reports, RPT_ERROR, "Could not read \"%s\"", filepath_startup_override);
   }
 
+  bool loaded_factory_settings = false;
   if (success == false) {
     BlendFileReadParams read_file_params{};
     read_file_params.is_startup = true;
@@ -1364,6 +1370,7 @@ void wm_homefile_read_ex(bContext *C,
       BKE_blendfile_read_setup_readfile(
           C, bfd, &read_file_params, wm_setup_data, &read_report, true, nullptr);
       success = true;
+      loaded_factory_settings = true;
       bmain = CTX_data_main(C);
     }
   }
@@ -1418,6 +1425,7 @@ void wm_homefile_read_ex(bContext *C,
   if (use_data) {
     /* Finalize handling of WM, using the read WM and/or the current WM depending on things like
      * whether the UI is loaded from the .blend file or not, etc. */
+    wm_setup_data->is_factory_startup = loaded_factory_settings;
     wm_file_read_setup_wm_finalize(C, bmain, wm_setup_data);
   }