1.修复 当数据很少，直方图无法生产时，出bug

2.修复 时间为DateTime.MinValue时，无法  -1，出错

Project.FLY.Thick.FilmCasting/FLY.Thick.FilmCasting.UI.DbViewer/Db/DbProfilePack.cs

@@ -288,8 +288,12 @@ namespace FLY.Thick.FilmCasting.UI.DbViewer.Db
                 }
             }
             if (all_datas.Count() == 0)
-                return null;
-
+            {
+                Histogram_TotalCount = 0;
+                Histogram_Sigma = double.NaN;
+                Histogram_Average = double.NaN;
+                return list;
+            }
 
 
             foreach (var thk in all_datas)

Project.FLY.Thick.FilmCasting/FLY.Thick.FilmCasting.UI.DbViewer/PgSelect.xaml.cs

@@ -130,7 +130,13 @@ namespace FLY.Thick.FilmCasting.UI.DbViewer
             DbEndTime = dbHelper.DbEndTime;
             DbBeginTime = dbHelper.DbBeginTime;
             EndDate = DbEndTime;
-            BeginDate = EndDate.AddDays(-1);
+            try
+            {
+                BeginDate = EndDate.AddDays(-1);
+            }
+            catch (Exception e) {
+                BeginDate = EndDate;
+            }
         }
         private async void SelectMonthPath()
         {