Client: Fix the lightmap blending stage for terrain surfaces

Forgot to commit this, but it's clear that the alpha channel should not be affecting the lighting stage as that's taking place prior to texture blending.

Core/NativeClient/WebGPU/Shaders/TerrainGeometryShader.wgsl

@@ -159,11 +159,11 @@ fn fs_main(in: VertexOutput) -> @location(0) vec4f {
 	let sunlightRayOrigin = -normalize(uPerSceneData.directionalLightDirection.xyz);
 	let sunlightColorContribution = max(dot(sunlightRayOrigin, normal), 0.0);
 	let directionalLightColor = sunlightColorContribution * sunlightColor;
-	let combinedLightContribution = clampToUnitRange(directionalLightColor + ambientColor) * lightmapTextureColor.a;
+	let combinedLightContribution = clampToUnitRange(directionalLightColor + ambientColor);
 
 	// Screen blending increases the vibrancy of colors (see https://en.wikipedia.org/wiki/Blend_modes#Screen)
 	let contrastCorrectionColor = clampToUnitRange(ambientColor + sunlightColor - (sunlightColor * ambientColor));
-	let fragmentColor = clampToUnitRange(in.color * contrastCorrectionColor * combinedLightContribution * diffuseTextureColor.rgb + lightmapTextureColor.rgb);
+	let fragmentColor = in.color * contrastCorrectionColor * combinedLightContribution * diffuseTextureColor.rgb * lightmapTextureColor.a + lightmapTextureColor.rgb;
 
 	// Should be a no-op if fog is disabled, since the fogFactor would be zero
 	let foggedColor = mix(fragmentColor.rgb, uPerSceneData.fogColor.rgb, in.fogFactor);