fix: Handle empty flash part list

This is used to clear the red flashing status we need to handle this differently for spec A

WPinternals/ViewModels/LumiaUnlockBootloaderViewModel.cs

@@ -2657,6 +2657,8 @@ namespace WPinternals
             UInt64 totalwritten = 0;
             int ProgressPercentage = 0;
 
+            if (FlashParts != null)
+            {
                 foreach (FlashPart Part in FlashParts)
                 {
                     InputStreamLength += (ulong)Part.Stream.Length;
@@ -2704,6 +2706,7 @@ namespace WPinternals
                         }
                     }
                 }
+            }
 
             UpdateWorkingStatus(null, null, 100, WPinternalsStatus.Flashing);
         }