Fix bug #884 in TimeEnvelope of samples/led-more-blinking-lights (#990)

- the method IsLastMultiple(int value) did not use _count to correctly decide when the value is last multiple. 
-  simplified all methods returning bool, instead of returning true/false, it returns directly result of if check.
- it was tested against code snippet included in the bug description to test expected behavior.

samples/led-more-blinking-lights/TimeEnvelope.cs

@@ -58,31 +58,16 @@ internal class TimeEnvelope
 
     public bool IsFirstMultiple(int value)
     {
-        if (_time == value)
-        {
-            return true;
-        }
-
-        return false;
+        return _time == value;
     }
 
     public bool IsLastMultiple(int value)
     {
-        if (_time - value == 0)
-        {
-            return true;
-        }
-
-        return false;
+        return _count - value == _time;
     }
 
     public bool IsMultiple(int value)
     {
-        if (_time % value == 0)
-        {
-            return true;
-        }
-
-        return false;
+        return _time % value == 0;
     }
 }
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