Don't show low battery tip when estimation is zero

It means invalid when estimation is zero. We should catch this case
int LowBatteryDetector and don't show it.

Change-Id: I01dd50616f54162a6688257f4bdb329dfa351bc5
Fixes: 110226028
Test: RunSettingsRoboTests

tests/robotests/src/com/android/settings/fuelgauge/batterytip/detectors/LowBatteryDetectorTest.java

@@ -105,6 +105,13 @@ public class LowBatteryDetectorTest {
         assertThat(mLowBatteryDetector.detect().isVisible()).isFalse();
     }
 
+    @Test
+    public void testDetect_timeEstimationZero_tipInvisible() {
+        mBatteryInfo.batteryLevel = 50;
+        mBatteryInfo.remainingTimeUs = 0;
+        assertThat(mLowBatteryDetector.detect().isVisible()).isFalse();
+    }
+
     @Test
     public void testDetect_noEarlyWarning_tipInvisible() {
         mBatteryInfo.remainingTimeUs = TimeUnit.DAYS.toMicros(1);