Change SMA smoothing to always include current point

It is the common practice, and it works that way on forward mode,
but in backward mode current point was excluded from the average.

src/Core/Utils.cpp

@@ -526,8 +526,8 @@ smooth_sma(QVector<double>&data, int pos, int window, int samples)
         break;
 
     case GC_SMOOTH_BACKWARD:
-        window_end=0;
-        window_start=window *-1;
+        window_end=1;
+        window_start=window *-1 + 1;
         break;
 
     case GC_SMOOTH_CENTERED: // we should handle odd/even size better