fix CharReaderFromSyncStream read characters less than chunkSize (#2108)

[itboy87]

There was an issue with CharReaderFromSyncStream. When attempting to read characters fewer than the specified chunkSize, it returns the maximum chunkSize data instead. I have set a minimum chunkSize limit to 8 because the decoder requires a minimum size of the maximum character size to decode. I believe the maximum character size in bytes is 4 bytes, but for safety, I used 8 bytes. Therefore, if anyone sets the chunkSize to less than 8, it will throw an exception.

• Created two new constants:

companion object {
       private const val DEFAULT_CHUNK_SIZE = 1024
       private const val MIN_CHUNK_SIZE = 8
}

• Check chunkSize and throw IllegalArgumentException exception if its less than MIN_CHUNK_SIZE

init {
  if (chunkSize < MIN_CHUNK_SIZE) throw IllegalArgumentException("chunkSize must be greater than $MIN_CHUNK_SIZE")
}

• Refactored buffer fill code to bufferUp() function. This function returns the number of bytes added to the buffer. If tempStringBuilder doesn't have enough characters to read, the function will attempt to read more into the buffer until the condition is met or the stream is empty.

This PR closes #2108

[soywiz]

URLText extra test should be done in a separate PR since it looks unrelated to this

[itboy87]

@soywiz ok i will update it.

[soywiz]

LGTM

[soywiz]

Thanks!