LibAudio: Make playing lossy flacs more truthful

Playing a lossy flac file resulted in hearing something
you'd not like to play.  Instead of your lovely bass, you had sounds
as if you put a CD-ROM disc to a CD player.

It turned out that the size for making signed values was too big,
making all the values unsigned.

I've used lossyWav[1] (the posix port[2] to be exact)
to generate such files.

[1]: https://wiki.hydrogenaud.io/index.php?title=LossyWAV
[2]: https://github.com/MoSal/lossywav-for-posix

Userland/Libraries/LibAudio/FlacLoader.cpp

@@ -596,7 +596,7 @@ Vector<i32> FlacLoaderPlugin::parse_subframe(FlacSubframeHeader& subframe_header
 
         samples.ensure_capacity(m_current_frame->sample_count);
         for (u32 i = 0; i < m_current_frame->sample_count; ++i) {
-            samples.unchecked_append(sign_extend(constant_value, subframe_header.bits_per_sample));
+            samples.unchecked_append(sign_extend(constant_value, subframe_header.bits_per_sample - subframe_header.wasted_bits_per_sample));
         }
         break;
     }
@@ -645,8 +645,7 @@ Vector<i32> FlacLoaderPlugin::decode_custom_lpc(FlacSubframeHeader& subframe, In
 
     // warm-up samples
     for (auto i = 0; i < subframe.order; ++i) {
-        decoded.unchecked_append(sign_extend(bit_input.read_bits_big_endian(subframe.bits_per_sample - subframe.wasted_bits_per_sample), subframe.bits_per_sample));
-        decoded[i] <<= subframe.wasted_bits_per_sample;
+        decoded.unchecked_append(sign_extend(bit_input.read_bits_big_endian(subframe.bits_per_sample - subframe.wasted_bits_per_sample), subframe.bits_per_sample - subframe.wasted_bits_per_sample));
     }
 
     // precision of the coefficients
@@ -695,7 +694,7 @@ Vector<i32> FlacLoaderPlugin::decode_fixed_lpc(FlacSubframeHeader& subframe, Inp
 
     // warm-up samples
     for (auto i = 0; i < subframe.order; ++i) {
-        decoded.unchecked_append(sign_extend(bit_input.read_bits_big_endian(subframe.bits_per_sample - subframe.wasted_bits_per_sample), subframe.bits_per_sample));
+        decoded.unchecked_append(sign_extend(bit_input.read_bits_big_endian(subframe.bits_per_sample - subframe.wasted_bits_per_sample), subframe.bits_per_sample - subframe.wasted_bits_per_sample));
     }
 
     decode_residual(decoded, subframe, bit_input);