Better search criterion for RTF INCLUDETEXT

When combining the internal doxygen documentation noty only the real INCLUDETEXT commands are joined but alsso an attempt is made to do this for the source code lines wheer INCLUDETEXT appears. This is prevented by slightly improving the search criterions.

Author: albert-github

src/rtfgen.cpp

@@ -2104,7 +2104,7 @@ static bool preProcessFile(Dir &d,const QCString &infName, TextStream &t, bool b
   {
     line+='\n';
     size_t pos;
-    if ((pos=prevLine.find("INCLUDETEXT"))!=std::string::npos)
+    if ((pos=prevLine.find("INCLUDETEXT \""))!=std::string::npos)
     {
       size_t startNamePos  = prevLine.find('"',pos)+1;
       size_t endNamePos    = prevLine.find('"',startNamePos);