Clamp oversized RIFF chunk to available bytes instead of rejecting it (#1329)

Some encoders write a valid data chunk but with a slightly too-large
declared chunkSize, or place the data chunk beyond the declared RIFF
boundary. The previous behaviour called break, abandoning all remaining
chunks and making the file appear empty to taglib.

Lenient parsers (ffmpeg, QuickTime) handle this case by clamping the
chunk size to the bytes that actually remain in the file. Adopt the
same strategy: when chunkSize would exceed the file length, clamp it
and continue parsing rather than stopping early.

tests/test_wav.cpp

@@ -320,7 +320,7 @@ public:
     {
       FileStream stream(copy.fileName().c_str());
       stream.seek(0, IOStream::End);
-      constexpr char garbage[] = "12345678";
+      constexpr char garbage[] = "\r2345678";
       stream.writeBlock(ByteVector(garbage, sizeof(garbage) - 1));
       stream.seek(0);
       contentsBeforeModification = stream.readBlock(stream.length());