UI: Fix studio mode transition bugs

-If the user were in the middle of a transition and clicked
the cut transition, the transitions would become borked.

-This actually disables the transition widgets, so the
user doesn't click them. Before, the disabling of the
widgets didn't work as expected. The code for enabling/disabling
them was also simplified.

-This loading of studio mode was moved in OBSInit because
the loading of transitions needs to happen first. This fixes
a bug when enabling/disabling the t-bar when the program
is first loaded. The t-bar would be disabled even if a
cut or stinger transition was not used.

-When the user would click the quick transitions, the
t-bar would be enabled even when it was not supposed
to.

UI/window-basic-main.cpp

@@ -1633,15 +1633,6 @@ void OBSBasic::OBSInit()
 	editPropertiesMode = config_get_bool(
 		App()->GlobalConfig(), "BasicWindow", "EditPropertiesMode");
 
-	if (!opt_studio_mode) {
-		SetPreviewProgramMode(config_get_bool(App()->GlobalConfig(),
-						      "BasicWindow",
-						      "PreviewProgramMode"));
-	} else {
-		SetPreviewProgramMode(true);
-		opt_studio_mode = false;
-	}
-
 #define SET_VISIBILITY(name, control)                                         \
 	do {                                                                  \
 		if (config_has_user_value(App()->GlobalConfig(),              \
@@ -1824,6 +1815,15 @@ void OBSBasic::OBSInit()
 
 	ui->sources->UpdateIcons();
 
+	if (!opt_studio_mode) {
+		SetPreviewProgramMode(config_get_bool(App()->GlobalConfig(),
+						      "BasicWindow",
+						      "PreviewProgramMode"));
+	} else {
+		SetPreviewProgramMode(true);
+		opt_studio_mode = false;
+	}
+
 #if !defined(_WIN32) && !defined(__APPLE__)
 	delete ui->actionShowCrashLogs;
 	delete ui->actionUploadLastCrashLog;