Idle::Start must be called with SolarMutex locked

...as asserted now since c00d8271ba443c4f0acf657c226eea4824597f95 "vcl: assert
solar mutex is held for various timer / scheduler ops."  Caused that assert to
fire when adding an extension via "Tools - Extension Manager... Add".

Change-Id: I86eeb2c4a83c3dff98ba9012c068af91e7932df6
(cherry picked from commit f108d9f088127050c641b1dd119d54179f4371e3)
Reviewed-on: https://gerrit.libreoffice.org/31354
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>
diff --git a/linguistic/source/lngsvcmgr.cxx b/linguistic/source/lngsvcmgr.cxx
index 20ea193..9ac9656 100644
--- a/linguistic/source/lngsvcmgr.cxx
+++ b/linguistic/source/lngsvcmgr.cxx
@@ -29,6 +29,7 @@
#include <com/sun/star/linguistic2/ProofreadingIterator.hpp>

#include <unotools/lingucfg.hxx>
#include <vcl/svapp.hxx>
#include <comphelper/processfactory.hxx>
#include <i18nlangtag/lang.h>
#include <i18nlangtag/languagetag.hxx>
@@ -479,17 +480,22 @@ LngSvcMgr::LngSvcMgr()
void LngSvcMgr::modified(const lang::EventObject&)
    throw(uno::RuntimeException, std::exception)
{
    osl::MutexGuard aGuard(GetLinguMutex());
    //assume that if an extension has been added/removed that
    //it might be a dictionary extension, so drop our cache
    {
        osl::MutexGuard aGuard(GetLinguMutex());
        //assume that if an extension has been added/removed that
        //it might be a dictionary extension, so drop our cache

    clearSvcInfoArray(pAvailSpellSvcs);
    clearSvcInfoArray(pAvailGrammarSvcs);
    clearSvcInfoArray(pAvailHyphSvcs);
    clearSvcInfoArray(pAvailThesSvcs);
        clearSvcInfoArray(pAvailSpellSvcs);
        clearSvcInfoArray(pAvailGrammarSvcs);
        clearSvcInfoArray(pAvailHyphSvcs);
        clearSvcInfoArray(pAvailThesSvcs);
    }

    //schedule in an update to execute in the main thread
    aUpdateIdle.Start();
    {
        SolarMutexGuard aGuard;
        //schedule in an update to execute in the main thread
        aUpdateIdle.Start();
    }
}

//run update, and inform everyone that dictionaries (may) have changed, this