Fix premature nullness assertions

Issue: #6910
PiperOrigin-RevId: 291721229

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/ts/H264Reader.java

@@ -560,12 +560,16 @@ public final class H264Reader implements ElementaryStreamReader {
       }
 
       private boolean isFirstVclNalUnitOfPicture(SliceHeaderData other) {
+        if (!isComplete) {
+          return false;
+        }
+        if (!other.isComplete) {
+          return true;
+        }
         // See ISO 14496-10 subsection 7.4.1.2.4.
         SpsData spsData = Assertions.checkStateNotNull(this.spsData);
         SpsData otherSpsData = Assertions.checkStateNotNull(other.spsData);
-        return isComplete
-            && (!other.isComplete
-                || frameNum != other.frameNum
+        return frameNum != other.frameNum
             || picParameterSetId != other.picParameterSetId
             || fieldPicFlag != other.fieldPicFlag
             || (bottomFieldFlagPresent
@@ -581,7 +585,7 @@ public final class H264Reader implements ElementaryStreamReader {
                 && (deltaPicOrderCnt0 != other.deltaPicOrderCnt0
                     || deltaPicOrderCnt1 != other.deltaPicOrderCnt1))
             || idrPicFlag != other.idrPicFlag
-                || (idrPicFlag && idrPicId != other.idrPicId));
+            || (idrPicFlag && idrPicId != other.idrPicId);
       }
     }
   }