Fixed the bug where the chrono would not reset if an effect was applied twice on the same image

AgraV2/EffectGrayScale.cs

@@ -23,6 +23,9 @@ namespace AgraV2
             if (inputBmp == null)
                 return null;
 
+            //This is important for when the user wants to re apply an effet
+            ProcessingDuration = new List<double>();
+
             Bitmap[] result = new Bitmap[] { useGetSetPixel(inputBmp), useByteArray(inputBmp), usePointers(inputBmp)};
             return result;
         }

AgraV2/EffectMedianFilter.cs

@@ -46,6 +46,12 @@ namespace AgraV2
         }
         public override Bitmap[] apply(Bitmap inputBmp)
         {
+            if (inputBmp == null)
+                return null;
+
+            //This is important for when the user wants to re apply an effet
+            ProcessingDuration = new List<double>();
+
             Bitmap[] result = new Bitmap[] { medianFilter(inputBmp) };
             return result;
         }