Fix FLAC interactions with PBA 'remaining capacity'

The comment sounds like it is worried the next header won't fit after
`limit` and before the end of `data`, but the code was previously only
checking the space between `position` and `limit`. This led to some
unnecessary copies.

Running the Robolectric `FlacExtractorTest.sample()` test in only the
'partial reads' and I/O errors case (worst case for this bug) results
in 57271 copies without this fix, and 19 copies with it.

Sample of the first 10 copies before this fix, showing a copy is made
for every byte read from the input:

```
W/ibaker: Making a copy. input.position=8881, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8882, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8883, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8884, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8885, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8886, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8887, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8888, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8889, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8890, data.length=32768, pos=1, lim=1
```

And the first 10 copies after the fix:

```
W/ibaker: Making a copy. input.position=41648, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=74401, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=107154, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=139907, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=172660, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=41648, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=74401, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=107154, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=139907, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=172660, data.length=32768, pos=32753, lim=32768
```

PiperOrigin-RevId: 738341007
(cherry picked from commit 71ff9c6)

Author: icbaker

libraries/extractor/src/main/java/androidx/media3/extractor/flac/FlacExtractor.java

@@ -310,9 +310,13 @@ private void getFrameStartMarker(ExtractorInput input) throws IOException {
       currentFrameFirstSampleNumber = nextFrameFirstSampleNumber;
     }
 
-    if (buffer.bytesLeft() < FlacConstants.MAX_FRAME_HEADER_SIZE) {
-      // The next frame header may not fit in the rest of the buffer, so put the trailing bytes at
-      // the start of the buffer, and reset the position and limit.
+    int remainingBufferCapacity = buffer.getData().length - buffer.limit();
+    if (buffer.bytesLeft() < FlacConstants.MAX_FRAME_HEADER_SIZE
+        && remainingBufferCapacity < FlacConstants.MAX_FRAME_HEADER_SIZE) {
+      // We're running out of bytes to read before buffer.limit, and the next frame header may not
+      // fit in the rest of buffer.data beyond buffer.limit, so we move the bytes between
+      // buffer.position and buffer.limit to the start of buffer.data, and reset the position and
+      // limit.
       int bytesLeft = buffer.bytesLeft();
       System.arraycopy(
           buffer.getData(), buffer.getPosition(), buffer.getData(), /* destPos= */ 0, bytesLeft);