Guard listener cleanup of BasicProviderImpl

Otherwise JunitTest_sfx2_complex dbgutil asserts especially on
Windows with:

ucrtbased!get_wide_winmain_command_line+0x296
ucrtbased!get_wide_winmain_command_line+0xe4
ucrtbased!wassert+0x1a
vcllo!ImplDbgTestSolarMutex+0x43
tllo!DbgTestSolarMutex+0x11d
svllo!SfxBroadcaster::RemoveListener+0x2e
svllo!SfxListener::~SfxListener+0x8f
basprovlo!basprov::BasicProviderImpl::~BasicProviderImpl+0x8f
...

Change-Id: Ia183436a92bc70ed5208364987b3e97e27b5bd6e
Reviewed-on: https://gerrit.libreoffice.org/63289Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
Tested-by: Jenkins

scripting/source/basprov/basprov.cxx

@@ -101,6 +101,8 @@ namespace basprov
 
     BasicProviderImpl::~BasicProviderImpl()
     {
+        SolarMutexGuard aGuard;
+        EndListeningAll();
     }