fix dynamic font crash if no available font size

scene/resources/dynamic_font.cpp

@@ -192,7 +192,7 @@ Error DynamicFontAtSize::_load() {
 		ERR_FAIL_V_MSG(ERR_FILE_CANT_OPEN, "Error loading font.");
 	}
 
-	if (FT_HAS_COLOR(face)) {
+	if (FT_HAS_COLOR(face) && face->num_fixed_sizes > 0) {
 		int best_match = 0;
 		int diff = ABS(id.size - ((int64_t)face->available_sizes[0].width));
 		scale_color_font = float(id.size) / face->available_sizes[0].width;