bugfix(w3d): Draw missing textures untextured where the pixels are read

A texture that fails to load is a 128x128 fill of half-transparent magenta.
Binding the white fallback instead only covers the draw path, and the terrain
does not take it: it composites its tile textures by reading their contents, so
the magenta lands in the terrain atlas itself. What renders after that is an
ordinary, valid texture that happens to contain magenta, which no missing-texture
check at bind time can catch - the reason the earlier fix left the terrain pink
while models came out clean.

Retail data references terrain tiles it never shipped - trstrtholecvr.tga - so on
the web that washed magenta across the ground wherever those tiles were used. It
is the "pink" this port was reported with, and it is absent from the branch the
port came from only because that branch never built the placeholder at all.

Hand out white on the web at the source instead, which covers the composite and
the draw path alike. Diagnosis does not suffer: every failure still writes
"Missing texture <reason>: <file>" to stderr, which on the web shows up in the
browser console - that is how the offending asset was identified. Other platforms
keep the magenta.

Author: githubawn

Core/Libraries/Source/WWVegas/WW3D2/missingtexture.cpp

@@ -85,7 +85,21 @@ void MissingTexture::_Deinit()
 
 void MissingTexture::Build_CPU_Texture_Mips(std::vector<TextureBaseClass::TextureMipSnapshot> &mips)
 {
+	// TheSuperHackers @bugfix githubawn 30/07/2026 These pixels are not only what a
+	// missing texture is drawn with - they are also what anything that reads a texture's
+	// contents gets back, and the terrain composites its tile textures that way. Retail
+	// data references terrain tiles it never shipped (trstrtholecvr.tga), so on the web
+	// the magenta was blended into the terrain atlas itself and no longer looked like a
+	// bound placeholder: it survived the missing-texture check at bind time, which is why
+	// selecting the white fallback there did not clear it. Hand out white on the web so
+	// the composite stays untextured instead. The failure is still reported - every one
+	// writes "Missing texture <reason>: <file>" to stderr, which lands in the browser
+	// console. Other platforms keep the magenta.
+#if defined(__EMSCRIPTEN__)
+	constexpr unsigned kMissingPixel = 0xFFFFFFFF;
+#else
 	constexpr unsigned kMissingPixel = 0x7FFF00FF;
+#endif
 	unsigned width = missing_image_width;
 	unsigned height = missing_image_height;
 	mips.clear();