Do not crash when window creation fails (e.g. running headless)

Signed-off-by: falkTX <falktx@falktx.com>

carla

@@ -1 +1 @@
-Subproject commit 604416bf33bcf16410e43009f6d94b86dd41afcd
+Subproject commit 62e17bf0e180ec97aa227f142fc3274602aa554f

dpf

@@ -1 +1 @@
-Subproject commit 044b74cb9326c82375ebd65a2020ad0565a19f8e
+Subproject commit 227a7015a85deeed52eb2c58456303c201674118

src/override/Window.cpp

@@ -603,9 +603,7 @@ static void Window__writeImagePNG(void* context, void* data, int size) {
 
 
 void Window::step() {
-	DISTRHO_SAFE_ASSERT_RETURN(internal->tlw != nullptr,);
-
-	if (vg == nullptr)
+	if (internal->tlw == nullptr || vg == nullptr)
 		return;
 
 	double frameTime = system::getTime();