LibAudio: Don't assume that a non-full span means EOF

Especially if buffered streams are involved, not filling the span
completely can also mean that we just ran out of filled buffer space and
we need to refill it on the beginning of the next read call.

Userland/Libraries/LibAudio/MP3Loader.cpp

@@ -233,8 +233,7 @@ ErrorOr<MP3::MP3Frame, LoaderError> MP3LoaderPlugin::read_frame_data(MP3::Header
     auto& buffer = maybe_buffer.value();
 
     size_t old_reservoir_size = m_bit_reservoir.size();
-    if (LOADER_TRY(m_bitstream->read(buffer)).size() != buffer.size())
-        return LoaderError { LoaderError::Category::IO, m_loaded_samples, "Could not find another whole frame." };
+    LOADER_TRY(m_bitstream->read_entire_buffer(buffer));
     if (m_bit_reservoir.write(buffer) != header.slot_count)
         return LoaderError { LoaderError::Category::IO, m_loaded_samples, "Could not write frame into bit reservoir." };