Don't post process on tiny render targets, fixes #19628

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -3599,7 +3599,7 @@ void RasterizerSceneGLES3::_post_process(Environment *env, const CameraMatrix &p
 		glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
 	}
 
-	if (!env || storage->frame.current_rt->flags[RasterizerStorage::RENDER_TARGET_TRANSPARENT]) {
+	if (!env || storage->frame.current_rt->flags[RasterizerStorage::RENDER_TARGET_TRANSPARENT] || storage->frame.current_rt->width < 4 || storage->frame.current_rt->height < 4) { //no post process on small render targets
 		//no environment or transparent render, simply return and convert to SRGB
 		glBindFramebuffer(GL_FRAMEBUFFER, storage->frame.current_rt->fbo);
 		glActiveTexture(GL_TEXTURE0);
@@ -4297,7 +4297,7 @@ void RasterizerSceneGLES3::render_scene(const Transform &p_cam_transform, const
 		glClearBufferfv(GL_COLOR, 0, clear_color.components); // specular
 	}
 
-	VS::EnvironmentBG bg_mode = (!env || (probe && env->bg_mode == VS::ENV_BG_CANVAS)) ? VS::ENV_BG_CLEAR_COLOR : env->bg_mode;
+	VS::EnvironmentBG bg_mode = (!env || (probe && env->bg_mode == VS::ENV_BG_CANVAS)) ? VS::ENV_BG_CLEAR_COLOR : env->bg_mode; //if no environment, or canvas while rendering a probe (invalid use case), use color.
 
 	if (env) {
 		switch (bg_mode) {