Do not display the individual tax block in the report for uniform taxes.

If the document only has full tax items, there is no need to show the
block of individual taxes on the pdf. That mistake in the detection is
fixed by this commit.

src/reportgenerator.cpp

@@ -219,10 +219,10 @@ void ReportGenerator::slotAddresseeSearchFinished( int )
   /* replace the placeholders */
   /* A placeholder has the format <!-- %VALUE --> */
 
-  ArchDocPositionList posList = mArchDoc->positions();
+  const ArchDocPositionList posList = mArchDoc->positions();
   QString h;
 
-  ArchDocPositionList::iterator it;
+  ArchDocPositionList::const_iterator it;
   int specialPosCnt = 0;
   int taxFreeCnt    = 0;
   int reducedTaxCnt = 0;
@@ -235,7 +235,7 @@ void ReportGenerator::slotAddresseeSearchFinished( int )
   DocPositionBase::TaxType ttype = DocPositionBase::TaxInvalid;
   for ( it = posList.begin(); it != posList.end(); ++it ) {
     ArchDocPosition pos (*it);
-    if( ttype == -1 ) {
+    if( ttype == DocPositionBase::TaxInvalid  ) {
       ttype = pos.taxType();
     } else {
       if( ttype != pos.taxType() ) { // different from previous one?