fix m3tal/csdvp-evolutionary-alogirthm-optimization#3

Mostly due to a bad vector access in the overriden operator<<

src/model/course.cpp

@@ -234,10 +234,13 @@ std::ostream& operator<<(std::ostream& Stream, const Course & c)
 {
     std::string s = "Course\n\tid:"+std::to_string(c.id())+"\n\tname:"+c.name()+"\n\tECTS: "+std::to_string(c.ects());
     std::string tf;
+    if(c.timeFrame().size() > 0)
+    {
         for(int i = 0; i < c.timeFrame().size()-1; i++)
             tf+=std::to_string(c.timeFrame().at(i))+" ; ";
         tf+=std::to_string(c.timeFrame().at(c.timeFrame().size()-1));
         s+="\n\tTimeFrames: ["+tf+"]";
+    }
     Stream << s;
     return Stream;
 }