Related tdf#105500: leaks in PaletteManager and SvxColorToolBoxControl

See comments of the bugtracker for more details
Again thank you Alex for very useful information about leaks!

Change-Id: I96743e8b167224f1bec73db5f2ba82536c7f23fa
Reviewed-on: https://gerrit.libreoffice.org/41265Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

svx/source/tbxctrls/PaletteManager.cxx

@@ -62,6 +62,7 @@ PaletteManager::PaletteManager() :
 
 PaletteManager::~PaletteManager()
 {
+    m_Palettes.clear();
 }
 
 void PaletteManager::LoadPalettes()

svx/source/tbxctrls/tbcontrl.cxx

@@ -2807,6 +2807,7 @@ void SvxColorToolBoxControl::EnsurePaletteManager()
 
 SvxColorToolBoxControl::~SvxColorToolBoxControl()
 {
+    m_xPaletteManager.reset(nullptr);
 }
 
 void SvxColorToolBoxControl::setColorSelectFunction(const ColorSelectFunction& aColorSelectFunction)