TechDraw: [skip ci] fix several gcc/clang warnings

-Wunused-private-field
-Wmaybe-uninitialized
-Wunused-parameter

src/Mod/TechDraw/App/DrawViewSpreadsheet.cpp

@@ -172,7 +172,7 @@ std::string DrawViewSpreadsheet::getSheetImage(void)
     std::string rowPart;
     boost::regex re{"([A-Z]*)([0-9]*)"};
     boost::smatch what;
-    int iRowStart, iRowEnd;
+    int iRowStart = 0, iRowEnd = 0;
     std::string sColStart, sColEnd;
     if (boost::regex_search(scellstart, what, re)) {
         if (what.size() < 3) {

src/Mod/TechDraw/Gui/QGIViewDimension.cpp

@@ -522,6 +522,7 @@ void QGIViewDimension::setGroupSelection(bool b)
 
 void QGIViewDimension::select(bool state)
 {
+    Q_UNUSED(state)
 //    setSelected(state);
 //    draw();
 }

src/Mod/TechDraw/Gui/TaskCosmeticLine.h

@@ -96,7 +96,7 @@ private:
     TechDraw::DrawViewPart* m_partFeat;
 
     std::string m_edgeName;
-    int m_edgeIndex;
+    //int m_edgeIndex;
     TechDraw::CosmeticEdge* m_ce;
     TechDraw::CosmeticEdge* m_saveCE;
     std::vector<Base::Vector3d> m_points;