Fix crash when bad VTT timestamp encountered

Issue: #3396

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=173868849

library/core/src/androidTest/assets/webvtt/typical_with_bad_timestamps

+WEBVTT # This comment is allowed
+
+# First timestamp is missing the 1/1000ths component, but parse anyway.
+00:00 --> 00:01.234
+This is the first subtitle.
+
+02.345 --> 00:03.456
+This is the second subtitle.
+
+0.0.0 --> 00:05.678
+This should be discarded (too many dots).
+
+00:06.789 --> not-a-timestamp
+This should be discarded (not a timestamp).

library/core/src/androidTest/java/com/google/android/exoplayer2/text/webvtt/WebvttDecoderTest.java

@@ -36,6 +36,7 @@ import java.util.List;
 public class WebvttDecoderTest extends InstrumentationTestCase {
 
   private static final String TYPICAL_FILE = "webvtt/typical";
+  private static final String TYPICAL_WITH_BAD_TIMESTAMPS = "webvtt/typical_with_bad_timestamps";
   private static final String TYPICAL_WITH_IDS_FILE = "webvtt/typical_with_identifiers";
   private static final String TYPICAL_WITH_COMMENTS_FILE = "webvtt/typical_with_comments";
   private static final String WITH_POSITIONING_FILE = "webvtt/with_positioning";
@@ -67,6 +68,17 @@ public class WebvttDecoderTest extends InstrumentationTestCase {
     assertCue(subtitle, 2, 2345000, 3456000, "This is the second subtitle.");
   }
 
+  public void testDecodeTypicalWithBadTimestamps() throws IOException, SubtitleDecoderException {
+    WebvttSubtitle subtitle = getSubtitleForTestAsset(TYPICAL_WITH_BAD_TIMESTAMPS);
+
+    // Test event count.
+    assertEquals(4, subtitle.getEventTimeCount());
+
+    // Test cues.
+    assertCue(subtitle, 0, 0, 1234000, "This is the first subtitle.");
+    assertCue(subtitle, 2, 2345000, 3456000, "This is the second subtitle.");
+  }
+
   public void testDecodeTypicalWithIds() throws IOException, SubtitleDecoderException {
     WebvttSubtitle subtitle = getSubtitleForTestAsset(TYPICAL_WITH_IDS_FILE);
 

library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttParserUtil.java

@@ -56,9 +56,13 @@ public final class WebvttParserUtil {
     String[] parts = timestamp.split("\\.", 2);
     String[] subparts = parts[0].split(":");
     for (String subpart : subparts) {
-      value = value * 60 + Long.parseLong(subpart);
+      value = (value * 60) + Long.parseLong(subpart);
     }
-    return (value * 1000 + Long.parseLong(parts[1])) * 1000;
+    value *= 1000;
+    if (parts.length == 2) {
+      value += Long.parseLong(parts[1]);
+    }
+    return value * 1000;
   }
 
   /**
@@ -74,7 +78,7 @@ public final class WebvttParserUtil {
     }
     return Float.parseFloat(s.substring(0, s.length() - 1)) / 100;
   }
-  
+
   /**
    * Reads lines up to and including the next WebVTT cue header.
    *