[pvr] use Refresh() instead of Update() to refresh directory listing

To get rid of the default value for strDirectory in Update() and to gain control of whether we want to clear the cache or not, this will use Refresh() instead of Update() in all PVR windows to refresh the directory listing.
[pvr] cleanup: removes forgotten commented code block
[addoncallbacks] check key is non-null before use
Merge pull request #5032 from jmarshallnz/addon_callbacks_nonnull

[addoncallbacks] check key is non-null before use
fix build when HAL is enabled
Merge pull request #5031 from xhaggi/pvr-window-refresh

[pvr] use Refresh() instead of Update() to refresh directory listing
[depends/ffmpeg] - fix sed (didn't work on osx) - this fixes pkgconfig from ffmpeg configure
WindowXML::LoadXML: fix checking result of CXBMCTinyXML::LoadFile()
[epg] fix implicit std::string constructor with NULL argument
[epg] refactor Update() method into constructor as it's never used elsewhere
Merge pull request #5037 from xhaggi/fix-epg-stdstring-crash

[epg] fix implicit std::string constructor with NULL argument
Merge pull request #5036 from Memphiz/fixffmpegsed

[depends/ffmpeg] - fix sed (didn't work on osx) - this fixes pkgconfig f...
[configure] properly detect if curl was compiled statically with openssl