ofz#5942 Out of memory

when missing a glyph in a grapheme we set the whole grapheme as missing.  There
can be a huge long grapheme and iterating through each missing codepoint
results in the whole range pushed back repeatedly as missing.

Change-Id: Ib7c283389ee2357eb3b4264c78e558955ebad1eb
Reviewed-on: https://gerrit.libreoffice.org/49223Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/source/gdi/sallayout.cxx

@@ -270,6 +270,12 @@ void ImplLayoutRuns::AddRun( int nCharPos0, int nCharPos1, bool bRTL )
         nCharPos1 = nTemp;
     }
 
+    if (maRuns.size() >= 2 && nCharPos0 == maRuns[maRuns.size() - 2] && nCharPos1 == maRuns[maRuns.size() - 1])
+    {
+        //this run is the same as the last
+        return;
+    }
+
     // append new run
     maRuns.push_back( nCharPos0 );
     maRuns.push_back( nCharPos1 );