Fix FTBFS with stricter C++11

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit 85dd54d9c5)

kmplot/kmplot/xparser.cpp

@@ -521,7 +521,7 @@ TQString XParser::functionMinValue(uint id)
 {
   int const ix = ixValue(id);
   if (ix==-1)
-    return int();
+    return TQString();
   return ufkt[ix].str_dmin;
 }
 
@@ -539,7 +539,7 @@ TQString XParser::functionMaxValue(uint id)
 {
   int const ix = ixValue(id);
   if (ix==-1)
-    return int();
+    return TQString();
   return ufkt[ix].str_dmax;
 }
 
@@ -557,7 +557,7 @@ TQString XParser::functionStartXValue(uint id)
 {
   int const ix = ixValue(id);
   if (ix==-1)
-    return int();
+    return TQString();
   return ufkt[ix].str_startx;
 }
 
@@ -575,7 +575,7 @@ TQString XParser::functionStartYValue(uint id)
 {
   int const ix = ixValue(id);
   if (ix==-1)
-    return int();
+    return TQString();
   return ufkt[ix].str_starty;
 }