Calculate shift value in seconds prior to cast

This is a fix to the fractional time-shift that was added in 2632b29

vortex-ui/src/main/java/mil/army/usace/hec/vortex/ui/ShifterWizard.java

@@ -377,7 +377,7 @@ private void timeShifterTask() {
         int toSeconds = timeUnit.toSeconds();
 
         // Cast is validated on step 2 of the wizard
-        long seconds = (long) value * toSeconds;
+        long seconds = (long) (value * toSeconds);
 
         Duration interval = Duration.ofSeconds(seconds);