Fix #2824, gcc 12.1 build issues (#2825)

* Update shadowvolumes.cpp

* Update stencil.cpp

examples/13-stencil/stencil.cpp

@@ -609,6 +609,9 @@ struct Group
 	{
 		m_vbh.idx = bgfx::kInvalidHandle;
 		m_ibh.idx = bgfx::kInvalidHandle;
+		m_sphere={};
+		m_aabb={};
+		m_obb={};
 		m_prims.clear();
 	}
 

examples/14-shadowvolumes/shadowvolumes.cpp

@@ -764,6 +764,10 @@ struct Group
 		m_numEdges = 0;
 		m_edges = NULL;
 		m_edgePlanesUnalignedPtr = NULL;
+		m_edgePlanes = NULL;
+		m_aabb={};
+		m_sphere={};
+		m_obb={};
 		m_prims.clear();
 	}