Fix flac coverart may not be displayed

[yn386]

This PR fixes following problem.

Problem:

Flac coverart may not be displayed.

moOde Version

Release 8.1.2

Environment

Raspi: Pi-3B 1.2 1GB
Audio: Pi HDMI 1

How to reproduce:

Play flac file that have 7 or more metadata block before PICTURE metablock.

Detail of changes:

To prevent corrupt header from causing endless loop, only first 7 metadata blocks are processed and others are ignored here:

moode/www/inc/Zend/Media/Flac.php

Lines 171 to 175 in 0fbbe1e

	// r44d exit loop if > 7 iterations
	$count++;
	if ($count > 7) {
	break;
	}

but sometimes flac has multiple APPLICATION metadata block like this

[STREAMINFO]
[VORBIS_COMMENT]
[SEEKTABLE]
[APPLICATION]
[APPLICATION]
[APPLICATION]
[APPLICATION]
[APPLICATION]
[PICTURE]
[PADDING]

This is not corrupted flac and compatible with flac specification.

So I made changes instead of counting metadata block to prevent endless loop with coruupted files.

• Check whether metadata indicates 'invalid'.
  According to the flac specification, BLOCK_TYPE 127 indicates 'invalid' to avoid confution with a frame sync code.
  So if metadata block type was 127, the flac is able to be regarded as corrupted file.

• Check whether current file offset is in the file.
  If Last-metadata-block flag is still 0 until the end of file, the flac is able to be regarded as corrupted file.

Effect:

Coverart is displayed when playing flac file that have 7 or more metadata block before PICTURE metablock.

[moodeaudio]

Looks like a nice fix :-)

I'll merge and test this weekend.