Fix logspam from AppIdleHistory on first boot

Before /data/system/users/0/app_idle_stats.xml has been created, it is
expected that it doesn't exist.  Log a simple debug message instead of
an error message with stacktrace.

Bug: 290410617
Test: booted Cuttlefish and checked logcat
Change-Id: I19a72e3bd74038e7447a2d47529022a68a13b1e9

apex/jobscheduler/service/java/com/android/server/usage/AppIdleHistory.java

@@ -61,6 +61,7 @@ import java.io.BufferedOutputStream;
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
+import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.FileReader;
 import java.io.IOException;
@@ -802,6 +803,9 @@ public class AppIdleHistory {
                     }
                 }
             }
+        } catch (FileNotFoundException e) {
+            // Expected on first boot
+            Slog.d(TAG, "App idle file for user " + userId + " does not exist");
         } catch (IOException | XmlPullParserException e) {
             Slog.e(TAG, "Unable to read app idle file for user " + userId, e);
         } finally {