crashtesting: imported junk as form field text

spec says "An unsigned integer that MUST be 0xFFFFFFFF" for version
so at least insist on that

Change-Id: I8c11659d86fe122b1c8f61b1bf99e7b4b53ff306
Reviewed-on: https://gerrit.libreoffice.org/71236
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

sw/source/filter/ww8/ww8par3.cxx

@@ -2140,13 +2140,17 @@ void WW8FormulaControl::FormulaRead(SwWw8ControlType nWhich,
     SvStream *pDataStream)
 {
     sal_uInt8 nField;
-    // nHeaderBype == version
-    sal_uInt32 nHeaderByte = 0;
 
     // The following is a FFData structure as described in
     // Microsoft's DOC specification (chapter 2.9.78)
-
-    pDataStream->ReadUInt32( nHeaderByte );
+    sal_uInt32 nVersion = 0;
+    pDataStream->ReadUInt32(nVersion);
+    // An unsigned integer that MUST be 0xFFFFFFFF
+    if (nVersion != 0xFFFFFFFF)
+    {
+        SAL_WARN("sw.ww8", "Parsing error: invalid header for FFData");
+        return; // bail out
+    }
 
     // might be better to read the bits as a 16 bit word
     // ( like it is in the spec. )