Fix incorrect failure code in screen_get_framebuffer_format

RenderingDevice::screen_get_framebuffer_format should return a value of
type RenderingDevice::FramebufferFormatID which is an alias of int64_t
but it returns Error::FAILED with a value of 1. The compiler does not
complain because both types are integers but 1 corresponds to a valid
FramebufferFormatID, meaning a certain failure condition is missed.

This commit changes it to the correct value, INVALID_ID.

servers/rendering/rendering_device.cpp

@@ -4260,7 +4260,7 @@ RenderingDevice::FramebufferFormatID RenderingDevice::screen_get_framebuffer_for
 	_THREAD_SAFE_METHOD_
 
 	HashMap<DisplayServer::WindowID, RDD::SwapChainID>::ConstIterator it = screen_swap_chains.find(p_screen);
-	ERR_FAIL_COND_V_MSG(it == screen_swap_chains.end(), FAILED, "Screen was never prepared.");
+	ERR_FAIL_COND_V_MSG(it == screen_swap_chains.end(), INVALID_ID, "Screen was never prepared.");
 
 	DataFormat format = driver->swap_chain_get_format(it->value);
 	ERR_FAIL_COND_V(format == DATA_FORMAT_MAX, INVALID_ID);