[cmyth] Free chanstr in cmyth_channel_destroy

Commit 9d115f3e3181ae73fedf3165fa2576661d875d7b introduced refmem for
chanstr. Therefore it has to be freed now in cmyth_channel_destroy to
prevent leaking memory.
[mythtv-cmyth] Fix missing free in MythChannel::Number

Commit 9d115f3e3181ae73fedf3165fa2576661d875d7b introduced refmem for
chanstr. Therefore it has to be freed now in cmyth_channel_destroy to
prevent leaking memory.
[mythtv-cmyth] Fix memory leak in MythDatabase::GetChannelGroups

The function cmyth_mysql_get_channelids_in_group writes the list of
channel ids for a channel group into an array of unsigned int.
The allocation is done using ref_alloc.
We have to call ref_release also for a channelCount of 0 because
ref_alloc will also allocate memory when called with size parameter of 0.
[cmyth] Free db settings in cmyth_database_destroy
[cmyth] Remove unnecessary calls to mysql_close in cmyth_db_check_connection

The mysql connection is already closed in cmyth_database_close.
[mythtv-cmyth] Prevent MythFile::Length from returning negative number

The function cmyth_file_length returns negative numbers in case of an
error. Since MythFile::Length returns an unsigned value, this might lead into
unexpected behavior.
[mythtv-cmyth] Return proper number of recordings in FillRecordings

The function PVRClientMythTV::FillRecordings has to return the number of
visible recordings. Seems to be caused by forgotten curly braces.
[cmyth] Fix memory leak in cmyth_conn_connect_path

The call to cmyth_file_create has been moved to the end of the function.
It hasn't been removed at its original place leading to a memory leak.