Prevent error when scrolling through time before setting apm

Author: Pedro Lucas Da Silva Cunha

src/VueCtkDateTimePicker/_subs/PickersContainer/_subs/TimePicker.vue

@@ -277,7 +277,7 @@
       onScrollHours: debounce(function (scroll) {
         const value = this.getValue(scroll)
         const hour = this.isTwelveFormat
-					? this.apm
+					? this.apm && this.apm.toLowerCase
 						? this.apm.toLowerCase() === 'am'
 							? value + 1
 							: (value + 1 + 12)