Enable seamless cubemap only if extension is present.

drivers/gles2/rasterizer_storage_gles2.cpp

@@ -5469,7 +5469,9 @@ void RasterizerStorageGLES2::initialize() {
 #ifdef GLES_OVER_GL
 	//this needs to be enabled manually in OpenGL 2.1
 
+	if (config.extensions.has("GL_ARB_seamless_cube_map")) {
 		glEnable(_EXT_TEXTURE_CUBE_MAP_SEAMLESS);
+	}
 	glEnable(GL_POINT_SPRITE);
 	glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);
 #endif