fix crashes when switch timelapse and vase mode

Signed-off-by: SoftFever <softfeverever@gmail.com>

src/libslic3r/PrintConfig.hpp

@@ -153,8 +153,8 @@ enum BrimType {
     btOuterAndInner,
 };
 
-enum TimelapseType {
-    tlTraditional,
+enum TimelapseType : int {
+    tlTraditional = 0,
     tlSmooth
 };