obs-ffmpeg: Don't use standard newlines in HTML error messages

Qt by default will render strings that contain new line characters as
plain text, bypassing the HTML renderer.

plugins/obs-ffmpeg/obs-ffmpeg-nvenc.c

@@ -250,7 +250,7 @@ static void on_init_error(void *data, int ret)
 
 	dstr_copy(&error_message, obs_module_text("NVENC.Error"));
 	dstr_replace(&error_message, "%1", av_err2str(ret));
-	dstr_cat(&error_message, "\r\n\r\n");
+	dstr_cat(&error_message, "<br><br>");
 
 	if (enc->gpu > 0) {
 		// if a non-zero GPU failed, almost always

plugins/obs-ffmpeg/obs-ffmpeg-video-encoders.c

@@ -26,7 +26,7 @@ bool ffmpeg_video_encoder_init_codec(struct ffmpeg_video_encoder *enc)
 					     enc->enc_name);
 				dstr_replace(&error_message, "%2",
 					     av_err2str(ret));
-				dstr_cat(&error_message, "\r\n\r\n");
+				dstr_cat(&error_message, "<br><br>");
 
 				obs_encoder_set_last_error(enc->encoder,
 							   error_message.array);