- never render the null texture.

Blood's ROR effects won't work if this is not done.

source/glbackend/gl_texture.cpp

@@ -42,6 +42,7 @@
 #include "v_font.h"
 #include "palettecontainer.h"
 #include "../../glbackend/glbackend.h"
+#include "texturemanager.h"
 
 // Test CVARs.
 CVAR(Int, fixpalette, -1, 0)
@@ -90,6 +91,7 @@ FHardwareTexture* GLInstance::CreateIndexedTexture(FGameTexture* tex)
 
 FHardwareTexture* GLInstance::CreateTrueColorTexture(FGameTexture* tex, int palid, bool checkfulltransparency, bool rgb8bit)
 {
+	if (tex == TexMan.GameByIndex(0)) return nullptr;
 	auto texbuffer = tex->GetTexture()->CreateTexBuffer(palid, checkfulltransparency? 0: CTF_ProcessData);
 	// Check if the texture is fully transparent. When creating a brightmap such textures can be discarded.
 	if (checkfulltransparency)