Resolves tdf#89129: crash when defining a specific relationship

Returns early if comparison matches so you can reduce iterator scope and avoid last test for logging.

/usr/include/c++/4.9/debug/safe_iterator.h:168:error: attempt to copy-
    construct an iterator from a singular iterator.

Objects involved in the operation:
iterator "this" @ 0x0x7fffffff3a30 {
type = N11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPPvNSt9__cxx19986vectorIS3_SaIS3_EEEEENSt7__debug6vectorIS3_S7_EEEE (mutable iterator);
  state = past-the-end;
  references sequence with type `NSt7__debug6vectorIPvSaIS1_EEE' @ 0x0x7fffffff4088
}
iterator "other" @ 0x0x7fffffff3a90 {
type = N11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPPvNSt9__cxx19986vectorIS3_SaIS3_EEEEENSt7__debug6vectorIS3_S7_EEEE (mutable iterator);
  state = singular;
  references sequence with type `NSt7__debug6vectorIPvSaIS1_EEE' @ 0x0x7fffffff4088
}

4  0x00002aaab193d6e9 in boost::void_ptr_iterator<__gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<void**, std::__cxx1998::vector<void*, std::allocator<void*> > >, std::__debug::vector<void*, std::allocator<void*> > >, ImplBtnDlgItem>::base (this=0x7fffffff3a90)
    at /home/julien/compile-libreoffice/libreoffice/workdir/UnpackedTarball/boost/boost/ptr_container/detail/void_ptr_iterator.hpp:121
5  0x00002aaab193d269 in boost::operator==<__gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<void**, std::__cxx1998::vector<void*, std::allocator<void*> > >, std::__debug::vector<void*, std::allocator<void*> > >, ImplBtnDlgItem, __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<void**, std::__cxx1998::vector<void*, std::allocator<void*> > >, std::__debug::vector<void*, std::allocator<void*> > >, ImplBtnDlgItem> (l=..., r=...)
    at /home/julien/compile-libreoffice/libreoffice/workdir/UnpackedTarball/boost/boost/ptr_container/detail/void_ptr_iterator.hpp:179
6  0x00002aaab193c2ca in ButtonDialog::RemoveButton (this=0x7fffffff3d90, nId=1) at /home/julien/compile-libreoffice/libreoffice/vcl/source/window/btndlg.cxx:340
7  0x00002aaad8ed109b in dbaui::ORelationTableView::lookForUiActivities (this=0x317ef30)
    at /home/julien/compile-libreoffice/libreoffice/dbaccess/source/ui/relationdesign/RelationTableView.cxx:342

Change-Id: Ied45c222c94d2a362075a3b1550b6092aad77c62
Reviewed-on: https://gerrit.libreoffice.org/14325Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>
Tested-by: Lionel Elie Mamane <lionel@mamane.lu>

vcl/source/window/btndlg.cxx

@@ -322,8 +322,7 @@ void ButtonDialog::AddButton( StandardButtonType eType, sal_uInt16 nId,
 
 void ButtonDialog::RemoveButton( sal_uInt16 nId )
 {
-    btn_iterator it;
-    for (it = maItemList.begin(); it != maItemList.end(); ++it)
+    for (btn_iterator it = maItemList.begin(); it != maItemList.end(); ++it)
     {
         if (it->mnId == nId)
         {
@@ -333,12 +332,11 @@ void ButtonDialog::RemoveButton( sal_uInt16 nId )
                 delete it->mpPushButton;
 
             maItemList.erase(it);
-            break;
+            return;
         }
     }
 
-    if (it == maItemList.end())
-        SAL_WARN( "vcl.window", "ButtonDialog::RemoveButton(): ButtonId invalid" );
+    SAL_WARN( "vcl.window", "ButtonDialog::RemoveButton(): ButtonId invalid" );
 }
 
 void ButtonDialog::Clear()