Wakelock durations are 0 instead of -1 if unused

Previously, wakelock max/current/total durations were initialized to -1,
instead of 0. So if, e.g., an app held a full wakelock but not a partial
wakelock, then the partial wakelock would return -1 for these data. This
cl changes that to be 0. The value will only be -1 if the data is not
tracked (as is currently the case for full and window wakelocks), in
which case if the wakelock was held, -1 will be given to signify the
lack of tracking.

Test: manually confirm 0 instead of -1 in batterystats dump.
Change-Id: I934022294ba5adafb2e4d9a5be1dc20aab045cb0
diff --git a/core/java/android/os/BatteryStats.java b/core/java/android/os/BatteryStats.java
index 1eb0a8c..37c153f 100644
--- a/core/java/android/os/BatteryStats.java
+++ b/core/java/android/os/BatteryStats.java
@@ -2756,9 +2756,9 @@
             long elapsedRealtimeUs, String name, int which, String linePrefix) {
         long totalTimeMicros = 0;
         int count = 0;
-        long max = -1;
-        long current = -1;
-        long totalDuration = -1;
+        long max = 0;
+        long current = 0;
+        long totalDuration = 0;
         if (timer != null) {
             totalTimeMicros = timer.getTotalTimeLocked(elapsedRealtimeUs, which);
             count = timer.getCountLocked(which);