Fix splash screen showing on startup with files loaded by scripts

Suppressing the splash was only done when passing in an argument from
the command line.

Remove G.file_loaded, as it is misleading, only set once on startup,
replace with G.relbase_valid which is used everywhere else to check
if the file path should be used.

source/blender/blenkernel/BKE_global.h

@@ -45,7 +45,6 @@ typedef struct Global {
 
   /** When set: `G_MAIN->name` contains valid relative base path. */
   bool relbase_valid;
-  bool file_loaded;
   bool save_over;
 
   /** Strings of recent opened files. */

source/creator/creator.c

@@ -551,7 +551,8 @@ int main(int argc,
     WM_exit(C);
   }
   else {
-    if (!G.file_loaded) {
+    /* When no file is loaded, show the splash screen. */
+    if (!G.relbase_valid) {
       WM_init_splash(C);
     }
     WM_main(C);

source/creator/creator_args.c

@@ -2008,8 +2008,6 @@ static int arg_handle_load_file(int UNUSED(argc), const char **argv, void *data)
     }
   }
 
-  G.file_loaded = 1;
-
   return 0;
 }