Fix system information updating during hyperjump

I experienced following crash, when tried to see star system information
during hyperjump:

Started hyperspacing...
pioneer: SmartPtr.h:28: T* SmartPtrBase<Derived, T>::operator->() const
[with Derived = RefCountedPtr<StarSystem>; T = StarSystem]: Assertion
`m_ptr' failed.
Aborted (core dumped)

This commit adds more accurate checks for case when current system is
not defined.
Add support for patterns to space stations
Merge pull request #3151 from fluffyfreak/station_patterns

Add support for patterns to space stations
Update Changelog.txt
Change to show buy and sell columns with different prices instead of just "price" column.
Change the GalacticView to use a hi-res colour galaxy bmp by Baobobafet
Replace the galaxy.bmp to galaxy_dense.png and then optimise the GetSectorDensity method.
Fixed using the wrong pointer type float to float[]
Switch back using a bmp since OSX will apparently load the galaxy differently apparently!
Add a comment explaining why it must be a bitmap and change to use the SDL_LoadBMP_RW to emphasise the point.
Merge pull request #3150 from rutsky/system_info_in_hyperjump_bug

Fix system information updating during hyperjump
Added Vladimir Rutsky
Update Changelog.txt
Add new authors to NameGen (bumps savegame).
Merge remote-tracking branch 'fluffyfreak/galaxy_refactor'
Forgot to add Changelog.
Basic GalaxyGenerator infrastructure
Move Sector generation code to SectorGeneratorStages.
Move StarSystem generation code to StarSystemGeneratorStages.
Avoid StarSystem's excessive list of Generator friends with a variant of the Attorney-Client pattern.