Enable GL R8I and R8UI texture formats.

src/renderer_gl.cpp

@@ -1551,6 +1551,8 @@ namespace bgfx { namespace gl
 			if (BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGL)
 			||  BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30) )
 			{
+				setTextureFormat(TextureFormat::R8I,     GL_R8I,      GL_RED_INTEGER,  GL_BYTE);
+				setTextureFormat(TextureFormat::R8U,     GL_R8UI,     GL_RED_INTEGER,  GL_UNSIGNED_BYTE);
 				setTextureFormat(TextureFormat::R16I,    GL_R16I,     GL_RED_INTEGER,  GL_SHORT);
 				setTextureFormat(TextureFormat::R16U,    GL_R16UI,    GL_RED_INTEGER,  GL_UNSIGNED_SHORT);
 //				setTextureFormat(TextureFormat::RG16,    GL_RG16UI,   GL_RG_INTEGER,   GL_UNSIGNED_SHORT);