Fix NPE setting drm scheme type

drmInitData can be null in DASH if all of the init data is
specified at the manifest level instead. I took a look at
injecting the manifest format into the extractors, so that
we can actually copy the scheme type into it, but that's
at least non-trivial enough to delay for a subsequent CL.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161956246

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java

@@ -678,7 +678,8 @@ import java.util.List;
           parent, position, size);
           parent, position, size);
       if (sampleEntryEncryptionData != null) {
       if (sampleEntryEncryptionData != null) {
         atomType = sampleEntryEncryptionData.first;
         atomType = sampleEntryEncryptionData.first;
-        drmInitData = drmInitData.copyWithSchemeType(sampleEntryEncryptionData.second.schemeType);
+        drmInitData = drmInitData == null ? null
+            : drmInitData.copyWithSchemeType(sampleEntryEncryptionData.second.schemeType);
         out.trackEncryptionBoxes[entryIndex] = sampleEntryEncryptionData.second;
         out.trackEncryptionBoxes[entryIndex] = sampleEntryEncryptionData.second;
       }
       }
       parent.setPosition(childPosition);
       parent.setPosition(childPosition);
@@ -857,7 +858,8 @@ import java.util.List;
           parent, position, size);
           parent, position, size);
       if (sampleEntryEncryptionData != null) {
       if (sampleEntryEncryptionData != null) {
         atomType = sampleEntryEncryptionData.first;
         atomType = sampleEntryEncryptionData.first;
-        drmInitData = drmInitData.copyWithSchemeType(sampleEntryEncryptionData.second.schemeType);
+        drmInitData = drmInitData == null ? null
+            : drmInitData.copyWithSchemeType(sampleEntryEncryptionData.second.schemeType);
         out.trackEncryptionBoxes[entryIndex] = sampleEntryEncryptionData.second;
         out.trackEncryptionBoxes[entryIndex] = sampleEntryEncryptionData.second;
       }
       }
       parent.setPosition(childPosition);
       parent.setPosition(childPosition);