simplify code and fix out of bounds read

Change-Id: I5be3a28d3d1ae43974f844d143a30bfd989cbe5b

test/source/sheet/xspreadsheets2.cxx

@@ -326,10 +326,10 @@ void XSpreadsheets2::importSheetToCopy()
 bool XSpreadsheets2::isExternalReference(const OUString& aDestContent, const OUString& aSrcContent )
 {
     OUString aStart("'file://");
-    const sal_Char* sSrcContent = OUStringToOString( aSrcContent, RTL_TEXTENCODING_UTF8 ).getStr();
 
-    return  (aDestContent.endsWithIgnoreAsciiCaseAsciiL(sSrcContent, aSrcContent.getLength()) // same cell address
-            && aDestContent.indexOf(aStart)==0 // starts with 'file://
+    CPPUNIT_ASSERT(aDestContent.startsWith(aStart));
+
+    return  (aDestContent.endsWithIgnoreAsciiCase(aSrcContent, NULL) // same cell address
             && aDestContent.indexOf(aSrcFileName)>0); // contains source file name
 }