Do not resetSearch if we're closing down

It's useless as it will be reset anyway on the close down procedure
and it will cause a crash if you are unlucky.

Reason:
  * In the document observers qset pageview comes before
  * We are closing and notifySetup with an empty vector
  * pageview empties its vector in notifySetip
  * part sees the notifySetup and resets the search
  * resetting the search calls another notifySetup with the non empty page vector
    that will be deleted asap when we go back to the first notifySetup

There are another billion ways to fix this:
 * Don't allow nested notifySetup
 * Clear the running searches before sending the first notifySetup
 * Empty the pagesVector before sending the first notifySetup
 * etc

But i feel this is the less invasive one (even if it may not be the most technically correct)

BUGS: 329582
FIXED-IN: 4.12.1

core/document.cpp

@@ -3400,6 +3400,10 @@ void Document::continueSearch( int searchID, SearchType type )
 
 void Document::resetSearch( int searchID )
 {
+    // if we are closing down, don't bother doing anything
+    if ( !d->m_generator )
+        return;
+
     // check if searchID is present in runningSearches
     QMap< int, RunningSearch * >::iterator searchIt = d->m_searches.find( searchID );
     if ( searchIt == d->m_searches.end() )