MythMusic: fix Coverity ID 1026166 Improper use of negative value

In Ripper::toggleTrackActive(MythUIButtonListItem *): Negative value can be
returned from function is not being checked before being used improperly

The only way this could be a problem is if item doesn't exist which is very
unlikely.
MythMusic: fix Coverity ID  1026169 Resource leak

In EditMetadataCommon::scanForImages() image was not being deleted.
MythMusic: fix Coverity ID  1026175,1026176,1026177 Uninitialized variables
AvfDecoder: fix several Coverity detected errors

* 1026172 Uninitialized scalar variable (fill).
* 1026173 Uninitialized scalar variable (total).
* 1026164 Division or modulo by zero - this looks like a false positive
          because m_inited will be false if m_sampleFmt is FORMAT_NONE
          which is the only way the division by 0 can happen.
MythMusic: fix Coverity ID 1026174 initialise several variables in ThumbFinder
mytharchivehelper: fix Coverity ID 1026163 remove some logically dead code
Fix hang in applications when threadpool thread fails to run.

In the event that a thread pool threads fails to start do not leave it
in the list of running threads which can lead to us waiting
indefinitely for it to finish in MThreadPool::waitForDone(). The fix
is to immediately remove the thread from the list of running threads
if IsRunning() is false immediately after calling start() - see
start() in qthread-unix.cpp. N.B. IsFinished() is false in this
scenario because the thread never started.

When this occurs, either because we've hit the system thread limit or
we've run out of memory QThread (on unix/linux) will print:
"QThread::start: Thread creation error: Resource temporarily
unavailable"

Shortly afterwards the thread calling MThreadPool::waitForDone() would
hang, in the case of the frontend this may be the UI thread in the
MythImage destructor.
MetadataImageDownload: fix Coverity ID  700237 Unchecked return value

In MetadataImageDownload::run(): Value returned from a function is not
checked for errors before being used
MythFontProperties: fix Coverity ID 700924 Uninitialized scalar field

In MythFontProperties::MythFontProperties(): A scalar field is not
initialized by the constructor.
Search: fix Coverity ID  700801 Uninitialized scalar field

In Search::Search(): Several scalar fields are not initialized
by the constructor.
RSSSite: fix Coverity ID 700800 Uninitialized scalar field

In RSSSite::RSSSite(): A scalar field is not initialized by the constructor.
LanguageSelection: fix Coverity ID 700798 Uninitialized pointer field

In LanguageSelection::LanguageSelection(): Several pointer fields are not
initialized in the constructor.
ResultItem: fix Coverity ID 700806 Uninitialized scalar field

In ResultItem::ResultItem(): Several scalar fields are not initialized
by the constructor.
MetadataLookup: fix Coverity ID 700886, 700885 Uninitialized scalar field

MetadataLookup::MetadataLookup(): Several scalar fields are not initialized by
the constructors.
fix Coverity ID 700887 Uninitialized scalar field

In ParentalLevelChangeCheckerPrivate::ParentalLevelChangeCheckerPrivate():
Several scalar fields are not initialized by the constructor.
VideoMetadata: fix Coverity ID  700888 Uninitialized pointer field

In VideoMetadata::SortKey::SortKey(): A pointer field is not initialized in
the constructor (false positive because it's a copy constructor so the field
will be copied anyway)
VideoMetadata: fix Coverity ID 700889 Uninitialized pointer field

In VideoMetadata::VideoMetadata(): A pointer field is not initialized in the
constructor (false positive because it's a copy constructor so the field will
be copied anyway)
fix Coverity IDs 746868, 700890 Uninitialized scalar/pointer field

In VideoScanner::VideoScanner(): A scalar field is not initialized by the
constructor.

In VideoScannerThread::VideoScannerThread(): A pointer field is not
initialized in the constructor.
fix Coverity IDs 700811,700812,700813,700814,700815 Uninitialized scalar fields
Fix GCC C++11 warning about narrowing conversion.