Fix unusable command line options since GTK+:3 migration.

https://github.com/TASVideos/desmume/pull/416
From: Ingo Saitz <Ingo.Saitz@stud.uni-hannover.de>
Date: Sun, 3 Jan 2021 16:00:38 +0100
--- a/desmume/src/commandline.cpp
+++ b/desmume/src/commandline.cpp
@@ -41,7 +41,8 @@
 , _load_to_memory(-1)
-, _play_movie_file(0)
-, _record_movie_file(0)
-, _cflash_image(0)
-, _cflash_path(0)
-, _gbaslot_rom(0)
+, nds_file("")
+, play_movie_file("")
+, record_movie_file("")
+, cflash_image("")
+, cflash_path("")
+, gbaslot_rom("")
 , _bios_arm9(NULL)
@@ -60,4 +61,4 @@
 , _texture_smooth(-1)
-, _slot1(NULL)
-, _slot1_fat_dir(NULL)
+, slot1("")
+, slot1_fat_dir("")
 , _slot1_fat_dir_type(false)
@@ -68,3 +69,3 @@
 #endif
-, _console_type(NULL)
+, console_type("")
 , _advanscene_import(NULL)
@@ -360,4 +361,4 @@
 		case OPT_SLOT2_CFLASH_IMAGE: cflash_image = optarg; break;
-		case OPT_SLOT2_CFLASH_DIR: _cflash_path = optarg; break;
-		case OPT_SLOT2_GBAGAME: _gbaslot_rom = optarg; break;
+		case OPT_SLOT2_CFLASH_DIR: cflash_path = optarg; break;
+		case OPT_SLOT2_GBAGAME: gbaslot_rom = optarg; break;
 
@@ -520,4 +521,5 @@
 
-	if((_cflash_image && _gbaslot_rom) || (_cflash_path && _gbaslot_rom)) {
+	if((cflash_image != "" && gbaslot_rom != "") || (cflash_path != "" && gbaslot_rom != "")) {
 		printerror("Cannot specify both cflash and gbaslot rom (both occupy SLOT-2)\n");
+		return false;
 	}
--- a/desmume/src/commandline.h
+++ b/desmume/src/commandline.h
@@ -88,7 +88,2 @@
 private:
-	char* _play_movie_file;
-	char* _record_movie_file;
-	char* _cflash_image;
-	char* _cflash_path;
-	char* _gbaslot_rom;
 	char* _bios_arm9, *_bios_arm7;
@@ -109,5 +104,2 @@
 #endif
-	char* _slot1;
-	char *_slot1_fat_dir;
-	char* _console_type;
 	char* _advanscene_import;
--- a/desmume/src/frontend/posix/gtk/main.cpp
+++ b/desmume/src/frontend/posix/gtk/main.cpp
@@ -3555,12 +3555,9 @@
 
-static void
-handle_open(GApplication *application,
-            GFile **files,
-            gint n_files,
-            const gchar *hint,
+static gint
+ignore_command_line(GApplication *application,
+            GApplicationCommandLine *command_line,
             gpointer user_data)
 {
-    configured_features *my_config = static_cast<configured_features*>(user_data);
-    my_config->nds_file = g_file_get_path(files[0]);
     common_gtk_main(application, user_data);
+    return 0;
 }
@@ -3584,6 +3581,5 @@
 
-  // TODO: pass G_APPLICATION_HANDLES_COMMAND_LINE instead.
-  GtkApplication *app = gtk_application_new("org.desmume.DeSmuME", G_APPLICATION_HANDLES_OPEN);
+  GtkApplication *app = gtk_application_new("org.desmume.DeSmuME", G_APPLICATION_HANDLES_COMMAND_LINE);
   g_signal_connect (app, "activate", G_CALLBACK(common_gtk_main), &my_config);
-  g_signal_connect (app, "open", G_CALLBACK(handle_open), &my_config);
+  g_signal_connect (app, "command-line", G_CALLBACK(ignore_command_line), &my_config);
   g_action_map_add_action_entries(G_ACTION_MAP(app),