STY: Small ComputeConfusionMarix clean-ups (kindly provided by Laurentiu Nicola)

The "count-insert" idiom is an antipattern that leads to searching the
element twice. Avoid that and also the 0 comparison a bit below.

In addition, cache the end iterators of the two maps. This is safe as
the iterators stay valid when the map is modified.

Modules/Applications/AppClassification/app/otbComputeConfusionMatrix.cxx

@@ -288,27 +288,17 @@ private:
         if ((labelRef != nodata) && (labelProd != nodata))
           {
           // If the current labels have not been added to their respective mapOfClasses yet
-          if (mapOfClassesRef.count(labelRef) == 0)
+          if (mapOfClassesRef.insert(MapOfClassesType::value_type(labelRef, itLabelRef)).second)
             {
-            mapOfClassesRef[labelRef] = itLabelRef;
             ++itLabelRef;
             }
-          if (mapOfClassesProd.count(labelProd) == 0)
+          if (mapOfClassesProd.insert(MapOfClassesType::value_type(labelProd, itLabelProd)).second)
             {
-            mapOfClassesProd[labelProd] = itLabelProd;
             ++itLabelProd;
             }
 
           // Filling of m_Matrix
-          if (m_Matrix[labelRef][labelProd] == 0)
-            {
-            m_Matrix[labelRef][labelProd] = 1;
-            }
-          else
-            {
-            m_Matrix[labelRef][labelProd]++;
-            }
-
+          m_Matrix[labelRef][labelProd]++;
           } // END if ((labelRef != nodata) && (labelProd != nodata))
         ++itRef;
         ++itInput;
@@ -325,9 +315,11 @@ private:
 
     // Filling ossHeaderRefLabels for the output file
     ossHeaderRefLabels << commentRefStr;
+
+    MapOfClassesType::iterator itMapOfClassesRefEnd = mapOfClassesRef.end();
     itMapOfClassesRef = mapOfClassesRef.begin();
     int indexLabelRef = 0;
-    while (itMapOfClassesRef != mapOfClassesRef.end())
+    while (itMapOfClassesRef != itMapOfClassesRefEnd)
       {
       // labels labelRef of mapOfClassesRef are already sorted
       labelRef = itMapOfClassesRef->first;
@@ -338,7 +330,7 @@ private:
 
       ossHeaderRefLabels << labelRef;
       ++itMapOfClassesRef;
-      if (itMapOfClassesRef != mapOfClassesRef.end())
+      if (itMapOfClassesRef != itMapOfClassesRefEnd)
         {
         ossHeaderRefLabels << separatorChar;
         }
@@ -352,9 +344,10 @@ private:
 
     // Filling ossHeaderProdLabels for the output file
     ossHeaderProdLabels << commentProdStr;
+    MapOfClassesType::iterator itMapOfClassesProdEnd = mapOfClassesProd.end();
     itMapOfClassesProd = mapOfClassesProd.begin();
     int indexLabelProd = 0;
-    while (itMapOfClassesProd != mapOfClassesProd.end())
+    while (itMapOfClassesProd != itMapOfClassesProdEnd)
       {
       // labels labelProd of mapOfClassesProd are already sorted
       labelProd = itMapOfClassesProd->first;
@@ -365,7 +358,7 @@ private:
 
       ossHeaderProdLabels << labelProd;
       ++itMapOfClassesProd;
-      if (itMapOfClassesProd != mapOfClassesProd.end())
+      if (itMapOfClassesProd != itMapOfClassesProdEnd)
         {
         ossHeaderProdLabels << separatorChar;
         }
@@ -402,13 +395,13 @@ private:
     // Initialization of m_MatrixLOG
     m_MatrixLOG.SetSize(nbClassesRef, nbClassesRef);
     m_MatrixLOG.Fill(0);
-    for (itMapOfClassesRef = mapOfClassesRef.begin(); itMapOfClassesRef != mapOfClassesRef.end(); ++itMapOfClassesRef)
+    for (itMapOfClassesRef = mapOfClassesRef.begin(); itMapOfClassesRef != itMapOfClassesRefEnd; ++itMapOfClassesRef)
       {
       // labels labelRef of mapOfClassesRef are already sorted
       labelRef = itMapOfClassesRef->first;
 
       indexLabelProd = 0;
-      for (itMapOfClassesProd = mapOfClassesProd.begin(); itMapOfClassesProd != mapOfClassesProd.end(); ++itMapOfClassesProd)
+      for (itMapOfClassesProd = mapOfClassesProd.begin(); itMapOfClassesProd != itMapOfClassesProdEnd; ++itMapOfClassesProd)
         {
         // labels labelProd of mapOfClassesProd are already sorted
         labelProd = itMapOfClassesProd->first;
@@ -458,7 +451,7 @@ private:
     confMatMeasurements->SetConfusionMatrix(m_MatrixLOG);
     confMatMeasurements->Compute();
 
-    for (itMapOfClassesRef = mapOfClassesRef.begin(); itMapOfClassesRef != mapOfClassesRef.end(); ++itMapOfClassesRef)
+    for (itMapOfClassesRef = mapOfClassesRef.begin(); itMapOfClassesRef != itMapOfClassesRefEnd; ++itMapOfClassesRef)
       {
       labelRef = itMapOfClassesRef->first;
       indexLabelRef = itMapOfClassesRef->second;