coverity#1038307 Negative loop bound

Change-Id: Ib0ca4fc350d84e25283e261cb9f48b0f6f22e81b
Reviewed-on: https://gerrit.libreoffice.org/4556Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>

editeng/source/editeng/impedit2.cxx

@@ -1893,6 +1893,9 @@ void ImpEditEngine::InitWritingDirections( sal_Int32 nPara )
 
         size_t nCount = ubidi_countRuns( pBidi, &nError );
 
+        /* ubidi_countRuns can return -1 in case of error */
+        if(nCount > 0)
+        {
             int32_t nStart = 0;
             int32_t nEnd;
             UBiDiLevel nCurrDir;
@@ -1903,6 +1906,7 @@ void ImpEditEngine::InitWritingDirections( sal_Int32 nPara )
                 rInfos.push_back( WritingDirectionInfo( nCurrDir, (sal_uInt16)nStart, (sal_uInt16)nEnd ) );
                 nStart = nEnd;
             }
+        }
 
         ubidi_close( pBidi );
     }