Use FImageTexture for thre null texture

FDummyTexture had a big problem: Whenever it was accessed by accident it crashed the app because it wasn't fully implemented.

What it should do is return empty pixels of the given size, and an unextended FImageTexture is doing just that.

src/textures/multipatchtexturebuilder.cpp

@@ -364,7 +364,7 @@ void FMultipatchTextureBuilder::AddTexturesLump(const void *lumpdata, int lumpsi
 			// It still needs to be created in case someone uses it by name.
 			offset = LittleLong(directory[1]);
 			const maptexture_t *tex = (const maptexture_t *)((const uint8_t *)maptex + offset);
-			FDummyTexture *tex0 = static_cast<FDummyTexture *>(TexMan.ByIndex(0));
+			FTexture *tex0 = TexMan.ByIndex(0);
 			tex0->SetSize(SAFESHORT(tex->width), SAFESHORT(tex->height));
 		}
 

src/textures/texture.cpp

@@ -761,26 +761,6 @@ TArray<uint8_t> FTexture::Get8BitPixels(bool alphatex)
 	return Pixels;
 }
 
-//===========================================================================
-// 
-// Dummy texture for the 0-entry.
-//
-//===========================================================================
-
-FDummyTexture::FDummyTexture ()
-{
-	Width = 64;
-	Height = 64;
-	UseType = ETextureType::Null;
-}
-
-void FDummyTexture::SetSize (int width, int height)
-{
-	Width = width;
-	Height = height;
-}
-
-
 //==========================================================================
 //
 // 

src/textures/texturemanager.cpp

@@ -1003,7 +1003,9 @@ void FTextureManager::Init()
 	FTexture::InitGrayMap();
 
 	// Texture 0 is a dummy texture used to indicate "no texture"
-	AddTexture (new FDummyTexture);
+	auto nulltex = new FImageTexture(nullptr);
+	nulltex->SetUseType(ETextureType::Null);
+	AddTexture (nulltex);
 	// some special textures used in the game.
 	AddTexture(CreateShaderTexture(false, false));
 	AddTexture(CreateShaderTexture(false, true));

src/textures/textures.h

@@ -382,7 +382,15 @@ protected:
 	float shaderspeed = 1.f;
 	int shaderindex = 0;
 
-
+	// This is only legal for the null texture!
+	void SetSize(int w, int h)
+	{
+		if (UseType == ETextureType::Null)
+		{
+			Width = w;
+			Height = h;
+		}
+	}
 
 	// Returns true if GetPixelsBgra includes mipmaps
 	virtual bool Mipmapped() { return true; }
@@ -657,14 +665,6 @@ public:
 
 };
 
-// A texture that doesn't really exist
-class FDummyTexture : public FTexture
-{
-public:
-	FDummyTexture ();
-	void SetSize (int width, int height);
-};
-
 
 // A texture that can be drawn to.
 class DCanvas;