Silence some gcc 7 warnings.

* Mark switch fallthrough
    (-Wfallthrough);
  * Initialize variables to avoid false positives
    (-Wmaybe-uninitialized);
  * Fudge indentation to avoid false positives
    (-Wmisleading-indentation).

src/draw.cpp

@@ -332,7 +332,7 @@ GraphicsWindow::Selection GraphicsWindow::ChooseFromHoverToSelect() {
 
     Group *activeGroup = SK.GetGroup(SS.GW.activeGroup);
     int bestOrder = -1;
-    int bestZIndex;
+    int bestZIndex = 0;
     for(const Hover &hov : hoverList) {
         hGroup hg = {};
         if(hov.selection.entity.v != 0) {

src/drawentity.cpp

@@ -297,7 +297,7 @@ void Entity::ComputeInterpolatingSpline(SBezierList *sbl, bool periodic) const {
                 // The wrapping would work, except when n = 1 and everything
                 // wraps to zero...
                 if(i > 0)     bm.A[i][i - 1] = eq.x;
-                              bm.A[i][i]     = eq.y;
+                /**/          bm.A[i][i]     = eq.y;
                 if(i < (n-1)) bm.A[i][i + 1] = eq.z;
             }
         }

src/graphicswin.cpp

@@ -703,7 +703,8 @@ void GraphicsWindow::MenuView(Command id) {
             if(SS.GW.LockedInWorkplane()) {
                 SS.GW.AnimateOntoWorkplane();
                 break;
-            }  // if not in 2d mode fall through and use ORTHO logic
+            }  // if not in 2d mode use ORTHO logic
+            // fallthrough
         case Command::NEAREST_ORTHO:
         case Command::NEAREST_ISO: {
             static const Vector ortho[3] = {

src/mouse.cpp

@@ -293,6 +293,7 @@ void GraphicsWindow::MouseMoved(double x, double y, bool leftDown,
             } else {
                 SS.GW.pending.hasSuggestion = false;
             }
+            // fallthrough
         case Pending::DRAGGING_NEW_POINT:
             UpdateDraggedPoint(pending.point, x, y);
             HitTestMakeSelection(mp);

src/render/rendergl3.cpp

@@ -277,7 +277,7 @@ void OpenGl3Renderer::InvalidatePixmap(std::shared_ptr<const Pixmap> pm) {
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
     }
 
-    GLenum format;
+    GLenum format = 0;
     switch(pm->format) {
         case Pixmap::Format::RGBA: format = GL_RGBA;  break;
         case Pixmap::Format::RGB:  format = GL_RGB;   break;
@@ -340,7 +340,7 @@ void OpenGl3Renderer::DoStippledLine(const Vector &a, const Vector &b, hStroke h
         return;
     }
 
-    const char *patternSeq;
+    const char *patternSeq = NULL;
     Stroke s = *stroke;
     s.stipplePattern = StipplePattern::CONTINUOUS;
     hcs = GetStroke(s);

src/resource.cpp

@@ -1068,8 +1068,9 @@ int PluralExpr::Token::Precedence() {
                     return 3;
 
                 case Op::NONE:
-                    ssassert(false, "Unexpected operator");
+                    ;
             }
+            ssassert(false, "Unexpected operator");
 
         case Type::QUERY:
         case Type::COLON: