tdf#92918 Engineering notation lost with Add/Delete Decimal Place

With scientific format, use the trick of thousand separator to detect
Engineering notation.

Change-Id: I7acdfb8bec646f9d6c1a17c334b60fa9708c8111
Reviewed-on: https://gerrit.libreoffice.org/17406Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>
(cherry picked from commit f4bdd798)
Reviewed-on: https://gerrit.libreoffice.org/17440

sc/source/ui/view/viewfunc.cxx

@@ -2543,6 +2543,12 @@ void ScViewFunc::ChangeNumFmtDecimals( bool bIncrement )
             nPrecision = aOut.getLength() - nPos - aDecSep.getLength();
         // else keep 0
     }
+    else
+    {
+        if ( (nOldType & css::util::NumberFormat::SCIENTIFIC) && !bThousand &&
+             (pOldEntry->GetFormatIntegerDigits()%3 == 0) && pOldEntry->GetFormatIntegerDigits() > 0 )
+            bThousand =  true;
+    }
 
     if (!bError)
     {