fix: uninitialized class variable

This specific boolean variable could be used uninitialized. Assigning it
a default value is cheap and it avoids the issue.

src/Mod/Sketcher/Gui/Command.cpp

@@ -1327,7 +1327,7 @@ private:
     CmdSketcherSnap& operator= (const CmdSketcherSnap&) = delete;
     CmdSketcherSnap& operator= (CmdSketcherSnap&&) = delete;
 
-    bool snapEnabled;
+    bool snapEnabled = true;
 };
 
 CmdSketcherSnap::CmdSketcherSnap()