FlacExtractor: add condition for zero-length reads

This improves readability by making clearer that reading no bytes from
the input in readFrames() is an expected case if the buffer is full.

PiperOrigin-RevId: 288711841

library/core/src/main/java/com/google/android/exoplayer2/extractor/flac/FlacExtractor.java

@@ -256,16 +256,19 @@ public final class FlacExtractor implements Extractor {
 
 
     // Copy more bytes into the buffer.
     // Copy more bytes into the buffer.
     int currentLimit = buffer.limit();
     int currentLimit = buffer.limit();
+    boolean foundEndOfInput = false;
+    if (currentLimit < BUFFER_LENGTH) {
       int bytesRead =
       int bytesRead =
           input.read(
           input.read(
               buffer.data, /* offset= */ currentLimit, /* length= */ BUFFER_LENGTH - currentLimit);
               buffer.data, /* offset= */ currentLimit, /* length= */ BUFFER_LENGTH - currentLimit);
-    boolean foundEndOfInput = bytesRead == C.RESULT_END_OF_INPUT;
+      foundEndOfInput = bytesRead == C.RESULT_END_OF_INPUT;
       if (!foundEndOfInput) {
       if (!foundEndOfInput) {
         buffer.setLimit(currentLimit + bytesRead);
         buffer.setLimit(currentLimit + bytesRead);
       } else if (buffer.bytesLeft() == 0) {
       } else if (buffer.bytesLeft() == 0) {
         outputSampleMetadata();
         outputSampleMetadata();
         return Extractor.RESULT_END_OF_INPUT;
         return Extractor.RESULT_END_OF_INPUT;
       }
       }
+    }
 
 
     // Search for a frame.
     // Search for a frame.
     int positionBeforeFindingAFrame = buffer.getPosition();
     int positionBeforeFindingAFrame = buffer.getPosition();