Adapt to C++2a std::span<>::index_type being unsigned size_t

...and no longer signed ptrdiff_t (which now caused -Werror,-Wsign-compare here)

Change-Id: I48234d9cc4c35583e3268441dcc21a03fab3e856
Reviewed-on: https://gerrit.libreoffice.org/69306
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sfx2/source/control/dispatch.cxx

@@ -20,7 +20,6 @@
 #include <config_features.h>
 
 #include <algorithm>
-#include <cstddef>
 #include <deque>
 #include <vector>
 
@@ -1546,7 +1545,7 @@ void SfxDispatcher::SetSlotFilter(SfxSlotFilterState nEnable,
 {
 #ifdef DBG_UTIL
     // Check Array
-    for ( std::ptrdiff_t n = 1; n < pSIDs.size(); ++n )
+    for ( o3tl::span<sal_uInt16 const>::index_type n = 1; n < pSIDs.size(); ++n )
         DBG_ASSERT( pSIDs[n] > pSIDs[n-1], "SetSlotFilter: SIDs not sorted" );
 #endif