tr_image: detect RED images

Author: illwieckz

src/engine/renderer/tr_image.cpp

@@ -1065,7 +1065,31 @@ void R_UploadImage( const char *name, const byte **dataArray, int numLayers, int
 		}
 	}
 
-	if ( internalFormat == GL_RGBA8 )
+	if ( internalFormat == GL_RGB8 )
+	{
+		c = image->width * image->height;
+		scan = dataArray[0];
+
+		bool hasRGB = false;
+
+		for ( i = 0; i < c * 4; i += 4 )
+		{
+			if ( scan[ i + 1 ] != 0 )
+			{
+				hasRGB = true;
+				break;
+			}
+
+			if ( scan[ i + 2 ] != 0 )
+			{
+				hasRGB = true;
+				break;
+			}
+		}
+
+		internalFormat = hasRGB ? GL_RGB8 : GL_RED;
+	}
+	else if ( internalFormat == GL_RGBA8 )
 	{
 		// scan the texture for each channel's max values
 		// and verify if the alpha channel is being used or not