Fix bug in SGMisc<T>:: normalizePeriodic()

SGMisc<T>::normalizePeriodic(min,max,value) returned zero for
all values less than min.
Example:
A call of normalizePeriodic(0,twopi(),-pi()) returned zero
where the correct value would be 3*pi().

simgear/math/SGMisc.hxx

@@ -65,7 +65,7 @@ public:
       return min;
     T normalized = value - range*floor((value - min)/range);
     // two security checks that can only happen due to roundoff
-    if (value <= min)
+    if (normalized <= min)
       return min;
     if (max <= normalized)
       return min;